Hi please zoom in to see it clearly, uh you don’t have to answer them all but it would be nice !!! (no links please)

Hi Please Zoom In To See It Clearly, Uh You Dont Have To Answer Them All But It Would Be Nice !!! (no

Answers

Answer 1

Answer:

3. (a) - is the answer most likely

4: (a)

5 (d or c)

6 (b)

Answer 2
Ya whatever the person above said :))

Related Questions

Two students are sitting 1.50 m apart. One student has a mass of 70.0 kg and
the other has a mass of 52.0 kg. What is the gravitational force between them?
A. 8.01 x 10-9
B. 1.08 x 10-2
C. 2.28 x 10-8

Answers

Answer:

B

Explanation:

Predicted height and total energy

Answers

Answer:

The predicted height is 2.809 meters, writing this in centimeters we get (1m = 100cm):

h = 2.809 m = (2.809)*(100cm) = 280.9 cm

And the total energy is:

E = 6.696 J

Explanation:

First let's see the problem.

We have an object of mass m = 274g which is thrown upwards with an initial velocity v0 = 6.991 m/s, in a place with a gravitational acceleration of g = 8.7 m/s^2

When the object is on the air, the only force acting on it will be the gravitational force, then the acceleration of the object will be equal to the gravitational acceleration, then we can write:

a(t) = -8.7 m/s^2

Where the negative sign is because this acceleration points down.

Now to get the velocity of the object we can integrate over time to get:

v(t) = (-8.7 m/s^2)*t + v0

Where v0 is a constant of integration, which is the initial velocity, then we can write this as:

v(t) = (-8.7 m/s^2)*t + 6.991 m/s

Now we can integrate again over the time to get the position equation.

p(t) = (1/2)*(-8.7 m/s^2)*t^2 + (6.991 m/s)*t + p0

Where p0 is the initial position, because the ball is being thrown from the ground, the initial position is 0.

Then the position equation is:

p(t) = (1/2)*(-8.7 m/s^2)*t^2 + (6.991 m/s)*t

Ok, now we know all the movement equations for the object.

The first thing we want to know is the maximum height of the object.

We know that the object reaches its maximum height when the velocity is zero (this is, the velocity stops being positive, meaning that the object stops going up, then in that time we have the maximum height)

We need to solve:

v(t) = 0m/s = (-8.7 m/s^2)*t + 6.991 m/s

(8.7 m/s^2)*t =  6.991 m/s

t =  6.991 m/s/( (8.7 m/s^2)  = 0.804 seconds

The maximum height of the object is given by:

p(0.804s) = (1/2)*(-8.7 m/s^2)*(0.804)^2 + (6.991 m/s)*(0.804) = 2.809 m

The maximum height of the object is 2.809 meters.

Now let's find the maximum energy.

Remember that the energy of an object can be written as the sum of the potential energy U and the kinetic energy K.

E = K + U

Such that for an object of mass m and velocity v, the kinetic energy is:

K = (1/2)*m*v^2

And for an object of mass m, at a height h from the ground and with gravitational acceleration g, the potential energy is:

U = m*g*h

Now, when the object is at its maximum height, the velocity is zero.

Then K = 0

And for conservation of energy, the total energy of the object becomes potential energy.

E = 0 + U

E = U

So if we find the potential energy at the maximum height of the object's path, we can find the total energy of the object.

We know that:

mass = m = 274g = 0.274 kg  (here i used that 1kg = 1000g)

height = h = 2.809 meters.

gravitational acceleration = g = 8.7 m/s^2

Then the potential energy at this point is:

U =  0.274 kg*(2.809 meters)*(8.7 m/s^2) = 6.696 J

This means that the total energy of the object is:

E = 6.696 J

a glass rod is given a positive charge by rubbing it with silk. how did the rod become positive ?

Answers

Answer:

When the glass rod is rubbed with silk, the silk strips electrons from the rod, leaving it a positive charge. When the hard rubber rod is rubbed with wool, it gains electrons from the wool, gaining a negative charge.

Explanation:

A 10 kg box initially at rest is pulled with a 50 N horizontal force for 4 m across a level surface. The force of friction
acting on the box is a constant 20 N. How much work is done by the gravitational force?
A. 03
OB. 10 J
C. 100
D. 50 J

Answers

Answer:

B i think

Explanation:

...

If each Coulomb of charge is given 20 Joules of energy, what is the voltage of the battery?
A. 20 V
B. 5 V
C. 10 V
D. Not enough info

Answers

Answer:

Explanation:

V = J/C

V = 20/1

= 20 v

Option A is the correct answer

Please solve for 15 points. Please don’t input a link.

Answers

Answer:

a). Single replacement.

Explanation:

Because one element replaces another element in a compound

An enormous thunderstorm covers Dallas-Ft. Worth. Your best friend Clark is a storm chaser and heads to the center of the storm to take some readings while you stay dry at home. While Clark is at the center of the storm, he sees and hears lightning strike a tree that is 150 m from where he is standing. You are 127 km from the tree. How long does it take for the sound to reach Clark

Answers

Answer:

t = 0.437 s

Explanation:

The speed of sound is a constant that is worth v = 343 m / s

           v = d / t

            t = d / v

the time it takes for the sound to reach Clark at d = 150 m is

           t = 150/343

           t = 0.437 s

This same sound takes much longer to reach you

          t₂ = 127 10³/343

          t₂ = 370 s

Which of the following could be an example of chemical weathering?

a. rocks tumbling against each other

​b. water seeping into the ground, dissolving the limestone to form a cave​

c. a waterfall boring out a whole in a rock under it

Answers

Answer: B

Explanation:

Answers A and C are examples of physical weathering while B is chemical weathering when water and lime mix it creates a reaction

2. Which of the following objects has the greatest momentum?
A) a 145 grain baseball hit at 45 m/s
B) a 1200 kg car driving 25 m/s
C) a 2.0 *10-2 kg snail moving al 3.0 * 104 m/s
D) a 500 kg horse galloping at 12.0 m/s

Answers

Answer:

B) a 1200 kg car driving 25 m/s

Explanation:

Momentum can be defined as the multiplication (product) of the mass possessed by an object and its velocity. Momentum is considered to be a vector quantity because it has both magnitude and direction.

Mathematically, momentum is given by the formula;

[tex] Momentum = mass * velocity [/tex]

This ultimately implies that, the mass of an object or body is directly proportional to its momentum. Thus, the higher the mass of an object or body, the greater would be its momentum and vice-versa.

By mere inspection of the data given, we can see that the object with the greatest amount of mass and velocity is the car weighing 1200 kilograms and moving at 25 meters per seconds.

Substituting into the formula, we have;

[tex] Momentum = 1200 * 25 [/tex]

Momentum = 30,000 Kgm/s

The photograph shows part of the Great Plains of North America. How do
plains form?
A. Magma rises at a divergent plate boundary.
B. Tectonic movements make folds and faults in the crust.
C. Continental plates slip past each other at a transform boundary.
D. Water, wind, or glaciers either remove or deposit crust.
SUBMIT
2 PREVIOUS

Answers

Answer:

Some plains form as ice and water erodes, or wears away, the dirt and rock on higher land. Water and ice carry the bits of dirt, rock, and other material, called sediment, down hillsides to be deposited elsewhere. As layer upon layer of this sediment is laid down, plains form. Volcanic activity can also form plains.

A substance whose shape can easily change is a

Answers

There are many. But if this is a chemistry question it’s liquid

The energy goes from _____ to the _____ above it.

Answers

Answer:

The energy goes from the ground state to the excited states above it.

A mom pushes her 19.3 kg daughter on the swing. If she gives her an initial velocity of 7.5 m/s at the bottom of the swing and the swing sits 0.6 m above the ground at it's lowest point, what height does she reach above the ground?

Answers

Answer:

3.17333333333? I hope I get it right

Explanation:

..................hello

Help me with this review question please.

Answers

Answer:

K E=( mv²)/2

=(60×3.5²)/2

=367.5J

a disk of radius 10 cm speeds up from rest. it turns 60 radians reaching an angular velocity of 15 rad/s. what was the angular acceleration?
b. how long did it take the disk to reach this velocity?​

Answers

Answer:

a) The angular acceleration is 1.875 radians per square second.

b) The time taken by the disk to reach the final angular speed is 8 seconds.

Explanation:

a) Let suppose that the disk accelerates uniformly, given that initial and final angular speed ([tex]\omega_{o}[/tex], [tex]\omega_{f}[/tex]), in radians per second, and change in angular position ([tex]\Delta \theta[/tex]), in radians, are known. The angular acceleration ([tex]\alpha[/tex]), in radians per square second, are found by using this expression:

[tex]\alpha = \frac{\omega_{f}^{2}-\omega_{o}^{2}}{2\cdot \Delta \theta}[/tex] (1)

If we know that [tex]\omega_{o} = 0\,\frac{rad}{s}[/tex], [tex]\omega_{f} = 15\,\frac{rad}{s}[/tex] and [tex]\Delta \theta = 60\,rad[/tex], then the angular acceleration of the disk is:

[tex]\alpha = \frac{\omega_{f}^{2}-\omega_{o}^{2}}{2\cdot \Delta \theta}[/tex]

[tex]\alpha = 1.875\,\frac{rad}{s^{2}}[/tex]

The angular acceleration is 1.875 radians per square second.

b) The time taken by the disk to reach the final angular velocity is determined by the following kinematic formula:

[tex]t = \frac{\omega_{f}-\omega_{o}}{\alpha}[/tex] (2)

Where [tex]t[/tex] is the time, in seconds.

If we know that [tex]\omega_{o} = 0\,\frac{rad}{s}[/tex], [tex]\omega_{f} = 15\,\frac{rad}{s}[/tex] and [tex]\alpha = 1.875\,\frac{rad}{s^{2}}[/tex], then the time taken by the disk is:

[tex]t = \frac{\omega_{f}-\omega_{o}}{\alpha}[/tex]

[tex]t = 8\,s[/tex]

The time taken by the disk to reach the final angular speed is 8 seconds.

A wheel rotates about a fixed axis with an initial angular velocity of 24 rad/s. During a 4 s interval the angular velocity decreases to 14 rad/s. Assume that the angular acceleration is constant during the 4 s interval. How many radians does the wheel turn through during the 4 s interval

Answers

Answer:

[tex]\theta=76\ rad[/tex]

Explanation:

Hoven that,

Initial angular velocity of the wheel = 24 rad/s

Final angular velocity = 14 m/s

Time, t = 4 s

We need to find how many radians does the wheel turn through during the 4 s interval. Let the displacement is [tex]\theta[/tex]. Using second equation of rotational kinematics to find it such that,

[tex]\theta=\omega_i t+\dfrac{1}{2}\alpha t^2[/tex]

Where

[tex]\alpha[/tex] is angular acceleration

[tex]\alpha =\dfrac{\omega_f-\omega_i}{t}\\\\\alpha =\dfrac{14-24}{4}\\\\\alpha =-2.5\ rad/s^2[/tex]

So,

[tex]\theta=24\times 4+\dfrac{1}{2}\times (-2.5)\times 4^2\\\\\theta=76\ rad[/tex]

So, it will turn 76 radian during the 4 s interval.

Please help me please with both questions

Answers

Answer:

6 - iron

7 - by stringing many magnets together

Explanation:

6 - substances such as iron, cobalt, and nickel, most of the electrons spin in the same direction. This makes the atoms in these substances strongly magnetic—but they are not yet magnets. ... The piece of iron has become a magnet. Some substances can be magnetized by an electric current.

7 - it is that only

A solenoid of 2100 turns, area 10 cm2, and length 30 cm carries a current of 4.0 A. (a) Calculate the magnetic energy stored in the solenoid from 1/2 LI 2. J [2 points] 0 attempt(s) made (maximum allowed for credit

Answers

Answer:

E = 0.1472  J

Explanation:

Given that,

The number of turns in the solenoid, N = 2100

Area of the solenoid, A = 10 cm² = 0.001 m²

The length of the solenoid, l = 30 cm = 0.3 m

Current in the solenoid, I = 4 A

We need to find the magnetic energy stored in the solenoid. The expression for the stored energy is :

[tex]E=\dfrac{1}{2}LI^2[/tex]

Where

L is self inductance of the solenoid,

[tex]L=\dfrac{\mu_oN^2A}{l}\\\\L=\dfrac{4\pi \times 10^{-7}\times 2100^2\times 0.001}{0.3}\\\\L=0.0184\ H[/tex]

So,

[tex]E=\dfrac{1}{2}\times 0.0184\times 4^2\\\\E=0.1472\ J[/tex]

So, 0.1472  J of energy is stored in the solenoid.

A horizontal 2.00\ m2.00 m long, 5.00\ kg5.00 kg uniform beam that lies along the east-west direction is acted on by two forces. At the east end of the beam, a 200\ N200 N forces pushes downward. At the west end of the beam, a 200\ N200 N force pushed upward. What is the angular acceleration of the beam

Answers

Answer: [tex]240\ rad/s^2[/tex]

Explanation:

Given

Length of beam [tex]l=2\ m[/tex]

mass of beam [tex]m=5\ kg[/tex]

Two forces of equal intensity acted in the opposite direction, therefore, they create a torque of magnitude

[tex]\tau =F\times l=200\times 2=400\ N.m[/tex]

Also, the beam starts rotating about its center

So, the moment of inertia of the beam is

[tex]I=\dfrac{ml^2}{12}=\dfrac{5\times 2^2}{12}\\\\I=\dfrac{5}{3}\ kg.m^2[/tex]

Torque is the product of moment of inertia and angular acceleration

[tex]\Rightarrow \tau=I\alpha\\\\\Rightarrow 400=\dfrac{5}{3}\times \alpha\\\\\Rightarrow \alpha =240\ rad/s^2[/tex]

A mass MM uniform solid cylinder of radius RR and a mass MM thin uniform spherical shell of radius RR roll without slipping. If both objects have the same kinetic energy, what is the ratio of the speed of the cylinder to the speed of the spherical shell

Answers

Answer:

vcyl / vsph = 1.05

Explanation:

The kinetic energy of a rolling object can be expressed as the sum of a translational kinetic energy plus a rotational kinetic energy.The traslational part can be written as follows:

       [tex]K_{trans} = \frac{1}{2}* M* v_{cm} ^{2} (1)[/tex]

The rotational part can be expressed as follows:

       [tex]K_{rot} = \frac{1}{2}* I* \omega ^{2} (2)[/tex]

where I = moment of Inertia regarding the axis of rotation.ω = angular speed of the rotating object.If the object has a radius R, and it rolls without slipping, there is a fixed relationship between the linear and angular speed, as follows:

       [tex]v = \omega * R (3)[/tex]

For a solid cylinder, I = M*R²/2 (4)Replacing (3) and (4)  in (2), we get:

       [tex]K_{rot} = \frac{1}{2}* \frac{1}{2} M*R^{2} * \frac{v_{cmc} ^{2}}{R^{2}} = \frac{1}{4}* M* v_{cmc}^{2} (5)[/tex]

Adding (5) and (1), we get the total kinetic energy for the solid cylinder, as follows:

       [tex]K_{cyl} = \frac{1}{2}* M* v_{cmc} ^{2} +\frac{1}{4}* M* v_{cmc}^{2} = \frac{3}{4}* M* v_{cmc} ^{2} (6)[/tex]

Repeating the same steps for the spherical shell:

        [tex]I_{sph} = \frac{2}{3} * M* R^{2} (7)[/tex]  

       [tex]K_{rot} = \frac{1}{2}* \frac{2}{3} M*R^{2} * \frac{v_{cms} ^{2}}{R^{2}} = \frac{1}{3}* M* v_{cms}^{2} (8)[/tex]

      [tex]K_{sph} = \frac{1}{2}* M* v_{cms} ^{2} +\frac{1}{3}* M* v_{cms}^{2} = \frac{5}{6}* M* v_{cms} ^{2} (9)[/tex]

Since we know that both masses are equal each other, we can simplify (6) and (9), cancelling both masses out.And since we also know that both objects have the same kinetic energy, this means that (6) are (9) are equal each other.Rearranging, and taking square roots on both sides, we get:

       [tex]\frac{v_{cmc}}{v_{cms}} =\sqrt{\frac{10}{9} } = 1.05 (10)[/tex]

This means that the solid cylinder is 5% faster than the spherical shell, which is due to the larger moment of inertia for the shell.

What causes an electric field?

Answers

Answer: The electric field is produced by stationary charges, and the magnetic field by moving charges (currents); these two are often described as the sources of the field. ... The force created by the electric field is much stronger than the force created by the magnetic field.

Explanation: An electric field is an invisible force field created by the attraction and repulsion of electrical charges (the cause of electric flow), and is measured in Volts per meter (V/m).

Answer:

The electric field is produced by stationary charges, and the magnetic field by moving charges (currents); these two are often described as the sources of the field.  The force created by the electric field is much stronger than the force created by the magnetic field.

Explanation:

Ggl

An airplane flies 1000 miles in 2 hours. What is its average speed in miles per hour?

Answers

Answer:

500km per hour

Explanation:

if in 2 hours the airplane flies 1000 km then 1000 divided by 2 is 500km per hour.

one negative change you may encounter as a student or an employee​

Answers

Answer:

you may get bullied or teased for being a differrent race, ethnic.

Answer:

Workload

Explanation:

You may feel stressed about a heavier workload or more too do. You will also be paid as an employee unlike, a student.

The angle between reflected ray and the normal line is

Answers

Answer:

Explanation:

angle of incidence.

Which nucleus completes the following equation?

Answers

Answer:

Option D. ²³⁹₉₃Np

Explanation:

From the question given above, the following data were:

²³⁹₉₂U —> ⁰₋₁e + __

Let ⁿₘX represent the unknown. Thus, the equation above becomes

²³⁹₉₂U —> ⁰₋₁e + ⁿₘX

Next, we shall determine n, m and X. This can be obtained as follow:

239 = 0 + n

239 = n

n = 239

92 = –1 + m

Collect like terms

92 + 1 = m

93 = m

m = 93

ⁿₘX => ²³⁹₉₃X => ²³⁹₉₃Np

Thus, the balanced equation becomes:

²³⁹₉₂U —> ⁰₋₁e + ⁿₘX

²³⁹₉₂U —> ⁰₋₁e + ²³⁹₉₃Np

Option D gives the correct answer to the question.

Answer:

D

Explanation:

239 93 Np

Please help guy review question.

Answers

Answer:

66.67 km/h

Explanation:

20 + 30 = 50

50/.75 = 66.67

I beg you plz help me asap!!!
Q. How does new planet change our understanding about the universe?​

Answers

Answer:

a.

Explanation:

there would be a new planet is our solar system which could cause different gravitation pull on all the planets also there could be possible be new life form or other valuable metals that haven't been discovered on this planet. hope this helps somewhat

Well, considering there's countless planets out there that haven't been discovered on top of the ones that have been, it definitely changes our understanding of the universe by showing that there's more out there to explore and the fact that conditions in space support a lot more planets than previously thought I'm sure.

Which of the following best describes wind?
A А
Sinking warm air moving a few feet above the ground
B
An air current formed by changes in ocean tides
с
Cool air rushing in to fill an area of low pressure
D
Rising warm air pushing cool air down toward Earth

Answers

The correct statement about the wind is:

Cool air rushing in to fill an area of low pressure

What is the wind?

Wind is the movement of air currents in relation to the Earth's surface, which is caused by pressure differences and air movement.

Characteristics of the wind

It is a meteorological phenomenon originated in the movements of rotation and translation of the Earth.

When the rising air cools and loses the moisture it was carrying, due to condensation and rain, the result is dry and cool air.

Therefore, we can conclude that the wind is the current of air that occurs in the atmosphere due to natural causes, from high pressure areas to low pressure areas.

Learn more about Characteristics of the wind here: https://brainly.com/question/11463167

What happens to warm air when it cools?
A
It sinks back down to Earth.
B
It is absorbed into clouds.
с
It remains in Earth's upper atmosphere.
D
It breaks apart and disappears.

Answers

Answer:

b I'm pretty sure sorry if I'm wrong

Answer:

I think the answer is B

Explanation:

The warm air turns cold and then it goes back to clouds

An object carries a +15.5 uC charge.
It is 0.525 m from a -7.25 uC charge.
What is the magnitude of the electric
force on the object?

Answers

Answer:

3.67 N

Explanation:

From the question given above, the following data were obtained:

Charge of 1st object (q₁) = +15.5 μC

Charge of 2nd object (q₂) = –7.25 μC

Distance apart (r) = 0.525 m

Force (F) =?

Next, we shall convert micro coulomb (μC) to coulomb (C). This can be obtained as follow:

For the 1st object

1 μC = 1×10¯⁶ C

Therefore,

15.5 μC = 15.5 × 1×10¯⁶

15.5 μC = 15.5×10¯⁶ C

For the 2nd object:

1 μC = 1×10¯⁶ C

Therefore,

–7.25 μC = –7.25 × 1×10¯⁶

–7.25 μC = –7.25×10¯⁶ C

Finally, we shall determine the force. This can be obtained as follow:

Charge of 1st object (q₁) = +15.5×10¯⁶ C

Charge of 2nd object (q₂) = –7.25×10¯⁶ C

Distance apart (r) = 0.525 m

Electrical constant (K) = 9×10⁹ Nm²/C²

Force (F) =?

F = Kq₁q₂ / r²

F = 9×10⁹ × 15.5×10¯⁶ × 7.25×10¯⁶ / 0.525²

F = 3.67 N

Therefore, the force on the object is 3.67 N

Other Questions
acrylonitrile, c3h3n, has the lewis structure shown in the figure. the molecule has ______ bonds and ______ bonds. If the federal government is issuing more block grants than categorical grants, what may be occurring?DevolutionNullificationIntimidationCoercion Find an orthogonal change of variables that eliminates the cross product terms in the quadratic form f(x, y) = x2 + 2xy + y2 and express it in terms of the new variables. (b) Use the result in part (a) to identify the conic section (ellipse, parabola or hyperbola) represented by the equation x2 + 2xy + y2 + 3x + y - 1 = 0. Sketch the graph of this conic section. A late penalty of 10% will apply to new answers. Intro ABC Corp. has just paid a quarterly dividend of 80.3. ABC's dividends will grow by 5% for the next 4 quarters, and then grow by 0.5% thereafter. ABC has a quarterly required return of 4%. IB- Attempt 1/10 for 9 pts. Part 1 What is the value of the stock? Find the mean and the variance of the finite popula tion that consists of the 10 numbers 15, 13, 18, 10, 6,21,7 11, 20, and 9. 17. Show that the variance of the finite population (c1,02,.. ,cN) can be written as i=1 Also, use this formula to recalculate the variance of the finite population of Two coils, held in fixed positions, have a mutual inductance of 100 H. What is the peak emf in one coil when the current in the other coil is i(t) = 10.0 sin (1.00 103t), where i is in amperes and t is in seconds? Buy a business Build a place and run it Franchise Work for an organization In your opinion which is a better option and why? Calculate the amount of energy needed to change 441 g of water ice at -10 degree Celsius to steam at 125 degree Celsius. The following constants may be useful:Cm (ice)=36.57 J/(molC)Cm (water)=75.40 J/(molC)Cm (steam)=36.04 J/(molC)Hfus=+6.01 kJ/molHvap=+40.67 kJ/molExpress your answer with the appropriate units. Which of the following integration types aims at reducing transaction costs? a. Vertical integrationb. Horizontal integrationc. Cointegrationd. Conglomerate integration Determine whether 548 is greater than or less than 373. Then write the expression showing this using < or >. A student was asked to find a 90% confidence interval for widget width using data from a random sample of size n - 23. Which of the following is a correct interpretation of the interval 12 < p A(n) ____________ is an object you can create that contains one or more variables known as fields.a. objectb. structurec. listd. container Question 1 (1 point) Which of the following occurs simultaneously with an income effect? Giffen good effect substitution effect backward-bending supply curve preferences effect The initial and final volumes during the process were Vi = 5 L and Vf = (Vi/2) L, respectively. If p0 = 4.4 atmL6/5, find the amount of work done on the gas, in joules. You are given an autonomous consumption is RM200, MPS is 0.8, investment is RM200 million, government expenditure is RM100 million and tax is 0.5Y, calculate the national income equilibrium? Select one: A. RM655.56 B. RM855.56 C. RM755.56 D. RM555.56 Rudyard Corporation had 230,000 shares of common stock and 23,000 shares of 5%, $100 par convertible preferred stock outstanding during the year. Net income for the year was $530,000 and dividends were paid to both common and preferred shareholders. Rudyard's effective tax rate is 25%. What is Rudyard's basic EPS? q1: how would you advise salgado to proceed on the issue of upgrading zaras pos systems? should the company upgrade the pos terminals to a modern operating system? what is an innovative feature of the minoan harvesters vase? War has broken out. You must train your workers to become soldiers. Decode this secret message to unlock a tomb full of artillery. What is the message about? Fur red bath dare bowls oogles boomings ekphrasis sandstone what is the rationale for the positive correlation between risk and expected return?