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Basic Physics Questions:

When you lift twice the load twice as high, in half the…

Complete Question Text:

When you lift twice the load twice as high, in half the time, the increase in potential energy is _______.

double

four times as much

three times as much

the same
When traveling twice as fast your kinetic energy is increased _______.

by two

by three

not at all

by four

In this problem, we will consider the following situation as depicted in the diagram (Figure 1) : A block of mass m slides at a speed valong a horizontal, smooth table. It next slides down a smooth ramp, descending a height h, and then slides along a horizontal rough floor, stopping eventually. Assume that the block slides slowly enough so that it does not lose contact with the supporting surfaces (table, ramp, or floor).
You will analyze the motion of the block at different moments using the law of conservation of energy.
Part A
Which word in the statement of this problem allows you to assume that the table is frictionless?

straight


smooth


horizontal
Suppose our experimenter repeats his experiment on a planet more massive than Earth, where the acceleration due to gravity is . When he releases the ball from chin height without giving it a push, how will the ball's behavior differ from its behavior on Earth? Ignore friction and air resistance. (Select all that apply.)

It will take less time to return to the point from which it was released.

It will stop well short of his face.

Its mass will be greater.

It will take more time to return to the point from which it was released.

It will smash his face.
Energy cannot be _______.
Energy cannot be _______.

transferred, transformed, or destroyed

transferred

destroyed

transformed
With the “Pulleys” slider set at 1, predict the minimum force needed to hoist the load.

300 N

75 N

slightly greater than 250 N

150 N
Do NOT move the force slider. With the “Pulleys” slider set at 1, predict the acceleration if the force exerted is 300 N.

2.0 m/s2

0.5 m/s2

1.0 m/s2

0.2 m/s2
Part C
How does the minimum force needed to hoist a load change as you increase the number of pulleys from one to two, to three, to four?

When the number of pulleys is increased from one to two, the minimum force needed to hoist the load becomes one-quarter; with three pulleys, the minimum force becomes one-ninth; and with four pulleys, the minimum force becomes one-sixteenth.

When the number of pulleys is increased from one to two, the minimum force needed to hoist the load is halved; with three pulleys, the minimum force becomes one-third; and with four pulleys the minimum force becomes one-fourth.

When the number of pulleys is increased from one to two, the minimum force needed to hoist the load does not change.
In a simple machine, how much work is done when an input of 10 N acts over a distance of 5 m?

10 J

5 J

50 J

15 J
A bow is drawn so that it has 40 J of potential energy. When fired, the arrow will ideally have a kinetic energy that is

less than 40 J.

40 J.

more than 40 J.

impossible to predict without additional information

After rolling halfway down an incline, a marble's kinetic energy is

less than its potential energy.

greater than its potential energy.

the same as its potential energy.

impossible to determine.
No work is done by gravity on a bowling ball that rolls along a bowling alley because

no potential energy is being converted to kinetic energy.

no force acts on the ball.

the force on the ball is at right angles to the ball's motion.

its kinetic energy remains constant.

no distance is covered by the ball.
A popular swinging-balls apparatus consists of an aligned row of identical elastic balls that are suspended by strings so they barely touch each other. When two balls are lifted from one end and released, they strike the row and two balls pop out from the other end. If instead one ball popped out with twice the speed of the two, this would be a violation of conservation of

energy.

momentum.

both of these

none of these
Is it easier to balance a long rod with a mass attached to it when the mass is closer to your hand or when the mass is farther away?

It is easier when the mass is farther from your hand.

It is equally easy in both cases.

It is easier when the mass is closer to your hand.
How does the rotational inertia of the rod with the mass toward the bottom compare with the rotational inertia of the mass toward the top?

The rotational inertia of the rod with the mass closer to the bottom is greater than the rotational inertia of the rod with the mass closer to the top.

The rotational inertia of the rod with the mass closer to the top is greater than the rotational inertia of the rod with the mass closer to the bottom.

The rotational inertia of the rod with the mass closer to the top is equal to the rotational inertia of the rod with the mass closer to the bottom.
Why does the rotational inertia of the rod with the attached mass closer to your hand compare the way it does with the rotational inertial of the rod with the attached mass farther away?


Rotational inertia depends on whether the mass is farther or closer to the point of rotation. The farther the mass is, the higher the rotational inertia.

Rotational inertia depends on whether the mass is lower or higher. Objects where the mass is higher have a greater rotational inertia.

Rotational inertia depends on whether the mass is farther or closer to the point of rotation. The closer the mass is, the higher the rotational inertia.
Is it easier for a circus performer to balance a long rod held vertically with people hanging off the other end, or the same long rod without the people at the other end, and why?

It is easier for the performer to balance a long rod held vertically with people at the other end because the rotational inertia is greater.

It is easier for the performer to balance a long rod held vertically with people at the other end because the rotational inertia is smaller.

It is easier for the performer to balance a long rod held vertically without people at the other end because the rotational inertia is greater.

It is easier for the performer to balance a long rod held vertically without people at the other end because the rotational inertia is smaller.
Rotational inertia about the midpoint of an object becomes greater with _______.
Rotational inertia about the midpoint of an object becomes greater with _______.

increased mass

decreased mass

decreased mass and decreased distance to mass concentration

increased mass and increased distance to mass concentration
Predict how the magnitude of the lever arm will change if you decrease the angle.

It increases.

It stays the same.

It decreases.
Predict how the lever arm will change when you decrease the distance.

It increases.

It stays the same.

It decreases.
Predict how the force needed to turn the wrench will change if you increase the lever arm.

It decreases.

It stays the same.

It increases.
Suppose we replace the mass in the video with one that is four times heavier. How far from the free end must we place the pivot to keep the meter stick in balance?

10 cm

25 cm

75 cm (25 cm from the weight)

90 cm (10 cm from the weight)

50 cm (in the middle)
Where is the center of gravity of the broom that Dr. Hewitt holds up?

at the center of the heavier side of the broom

at the balance point

at the center of the broom
When Dr. Hewitt cuts the broom right through the center of gravity, how do the weights of the two sides of the broom compare?

Both sides of the broom on either side of the center of gravity have equal weight.

The longer side (the handle) has a greater weight than the bristle side.

The shorter side, where the bristles of the broom are, has a greater weight than the handle.
How does the torque due to the weight of one side of the broom exerted around the balance point compare with the torque exerted by the weight of the other side of the broom around the balance point?

The torque due to the weight of the shorter side (the bristles of the broom) is smaller in magnitude than the torque due to the weight of the longer side, and opposite in direction.

The torque due to the weight of the shorter side (the bristles of the broom) is equal in magnitude to the torque due to the weight of the longer side, and opposite in direction.

The torque due to the weight of the shorter side (the bristles of the broom) is larger in magnitude than the torque due to the weight of the longer side (the handle), and opposite in direction.
The torque exerted by a crowbar on an object increases with increased _______.

energy of application

force and leverage distance

rotational inertia

force
When a rock tied to a string is whirled in a horizontal circle, doubling the speed _______.

decreases the velocity

doubles the velocity, but the string tension remains the same

doubles the tension in the string

quadruples the tension in the string
Consider someone in a rotating space habitat. The outward force felt by the person _______.

is a form of gravity

is an interaction with Earth

is real in the traditional sense

has no reaction counterpart
What is required to change the angular momentum of a system?
What is required to change the angular momentum of a system?

External force

External torque

Torque

Force
The experimenter from the video rotates on his stool, this time holding his empty hands in his lap. You stand on a desk above him and drop a long, heavy bean bag straight down into his hands. What happens?
The experimenter from the video rotates on his stool, this time holding his empty hands in his lap. You stand on a desk above him and drop a long, heavy bean bag straight down into his hands. What happens?

He spins faster.

He spins slower.

He continues spinning at the same speed.

It's not possible to predict what will happen.
When the rotational speed of a rotating system doubles, its angular momentum _______.

remains unchanged

doubles

reduces to zero

quadruples
An automobile speedometer is configured to read speed proportional to the rotational speed of its wheels. If larger wheels, such as those of snow tires, are used, will the speedometer reading be high, or low-or no different?

low

high

no different
The centers of gravity of the three trucks parked on a hill are shown by the Xs. Which truck(s) will tip over?
(Figure 1)
Check all that apply.

the left truck

the middle truck

the right truck
A ball rolls down a hill mainly because of

an unbalanced torque.

its angular momentum.

a balanced torque.

its angular acceleration.

its rotational inertia
For a system in mechanical equilibrium

the resultant forces and torques must be equal.

the resultant torques must be zero.

the resultant force must be zero.

the resultant forces and torques must both be zero.
A ring and a disk, initially at rest, roll down a hill together. The one to reach the bottom first

is the disk.

depends on the relative rotational inertias.

depends on the masses.

is the ring.

Both reach the bottom at the same time.

Show more
Asked on March 6, 2014, 8:56 p.m.

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