Test 3

What will be the kinetic energy of a pile driver ram starting from rest that undergoes a 10 kJ decrease in potential energy?

10 kJ

L =960 kg⋅m2/s

80-kg person sits 3.0 m from the center of a horizontally rotating platform with a tangential speed of 4.0 m/s. What is the angular momentum of the person? ( AM=mvr)

30% of the energy input to useful work—70% of the energy input will be wasted.

A certain machine is 30% efficient. This means the machine will convert

Disk

A hoop and a disk (thin solid cylinder) of the same mass and same diameter are released from the top of an incline at the same time. Which one will reach the bottom first?

20 RPM, 12 cm/s

A ladybug sits halfway between the rotational axis and the outer edge of the turntable. When the turntable has a rotational speed of 20 RPM and the bug has a tangential speed of 6 cm/s, what will be the rotational and tangential speeds of her friend who sits at the outer edge?

1000 W

A motor is used to pull a 100 kg palate to the second story of a building 10 m above the ground in 10 s. How much power did the motor exert?

10,000 J

A motor is used to pull a 100 kg palate to the second story of a building 10 m above the ground. How much work did the motor do?

K increases;U decreases; E stays the same

As the block slides down the ramp, what happens to its kinetic energy K potential U total mechanical E

KE = 1.7×104 J

Calculate the kinetic energy of a 108-kg scooter moving at 18 m/s. (KE =1/2 mv^2)

τ =8.8 N⋅m

Calculate the torque produced by a 40-N perpendicular force at the end of a 0.22-m longwrench. (Torque = Lever Arm × Force)

ΔU =−mgh

Considering that the potential energy of the block at the table is mgh/3 and that on the floor is −2mgh/3−what is the change in potential energy ΔU of the block if it is moved from the table to the floor?

v = √2gh

Emily drops a banana of mass (m) over the edge of a bridge of height (h) and it falls to the river below. From the initial PE of the banana converting to KE, find the speed of the banana just before hitting the water.

destroyed

Energy cannot be created or ______.

the Sun

Fossil fuels, hydroelectric power, and wind power ultimately get their energy from _______.

Angular momentum depends on the distribution of mass, whereas linear momentum depends on the total mass.

How do linear momentum and angular momentum differ?

It decreases.

How does the force needed to turn the wrench change if you increase the lever arm?

It decreases.

How does the lever arm change if you decrease the angle of the force?

It decreases.

How does the lever arm change when you decrease the distance to the nut?

U =−2mgh/3

If the zero level is a distance 2h/32h/3 above the floor, what is the potential energy UU of the block on the floor?

300 J

If you push a crate horizontally with 100 NN across a 10-mm factory floor and friction between the crate and the floor is a steady 70 NN, how much kinetic energy is gained by the crate?

25cm

In an ideal pulley system, a woman lifts a 100-N crate by pulling a rope downward with a force of 25 N. For every 1-meter length of rope she pulls downward, the crate rises

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.

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?

doubles

Suppose by pulling the weights inward, the rotational inertia of the man reduces to half its value. By what factor would his angular velocity change?

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

Suppose our experimenter repeats his experiment on a planet more massive than Earth, where the acceleration due to gravity is g=30 m/s2. 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.

a distance 2h/32h/3 above the floor

Suppose the potential energy of the block at the table is given by mgh/3mgh/3. This implies that the chosen zero level of potential energy is __________.

at the same rate

Suppose we replace both hover pucks with pucks that are the same size as the originals but twice as massive. Otherwise, we keep the experiment the same. Compared to the pucks in the video, this pair of pucks will rotate

at its geometrical center

The center of gravity of a basketball is located _______.

m =1.9 kg

The rock and meterstick balance at the 25-cm mark,. The meterstick has a mass of 1.9 kg. What must be the mass of the rock?

greater than toward the center

The tangential speed on the outer edge of a rotating carousel is _______.

force and leverage distance

The torque exerted by a crowbar on an object increases with increased _______.

90m

The work done in bringing a moving car to a stop is the force of tire friction stopping distance. If a particular car has a stopping distance of 10 m when moving at 10 m/s, what is its stopping distance when moving 30 m/s?

2.5 m

The work done in bringing a moving car to a stop is the force of tire friction stopping distance. If a particular car has a stopping distance of 10 m when moving at 10 m/s, what is its stopping distance when moving 5 m/s?

four times as much

The work that is done when twice the load is lifted twice the distance is _______.

vb =√(v2+2gh)

Using conservation of energy, find the speed vbvb of the block at the bottom of the ramp.

friction

What force is responsible for the decrease in the mechanical energy of the block?

The ball returns to Dr. Hewitt, stopping almost exactly at the point where it was released.

What happens the first time Dr. Hewitt lifts the bowling ball near his teeth and lets go?

The cord's tension on the right side of the pulley is higher than on the left side.

What happens when block B moves downward?

the same

When one does twice the work in twice the time, the power expended is _______.

50 percent

When the useful energy output of a simple machine is 100 J, and the total energy input is 200 J, the efficiency is _______.

four times

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

four times

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

Toward the center of the circle.

When you whirl a can overhead by a string in a circular path, what is the direction of the force exerted on the can?

at the balance point

Where is the center of gravity of the broom that Dr. Hewitt holds up?

The angular acceleration of the pulley is nonzero.

Which of the following statements correctly describes the system shown in the figure?

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.

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?

The minimum force needed to hoist the load becomes half, then one-third, then one-fourth

How does the minimum force needed to hoist a load change as you increase the number of pulleys from one to two, then three, then four?

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.

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?

W = 1600 J

How much work is done when you push a crate horizontally with 130 N across a 12-m factory floor?

Four times

Suppose you double the speed at which you round a bend in the curve, by what factor must the centripetal force change to prevent you from skidding?

Double

Suppose you take a sharper turn than before and halve the radius, by what factor must the centripetal force change to prevent you from skidding?

he spins slower

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 so that it lands across his lap, in his hands. What happens?

The ball leaves Dr. Hewitt and returns to him, going past the point where it was released.

What happens the second time Dr. Hewitt lifts the bowling ball near his teeth and gives it a push?

External torque

What is required to change the angular momentum of a system?

The shorter side, where the bristles of the broom are, has a greater weight than the handle.

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

12mv2i+mghi=12mv2f+mghf

Which most simplified form of the law of conservation of energy describes the motion of the block when it slides from the top of the table to the bottom of the ramp?

smooth

Which word in the statement of this problem allows you to assume that the table is frictionless?

The extra energy from the push is converted into kinetic energy, which is then converted into more potential energy at the end of the motion than the ball had when it was released.

Why does the bowling ball behave as it does when Dr. Hewitt lifts it and gives it a push?

All of the initial energy of the ball was converted completely back to potential energy when the ball returned.

Why does the bowling ball behave the way it does the first time Dr. Hewitt lifts the bowling ball near his teeth and lets go?

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.

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?

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

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?

The travel distance of the load becomes half, then one-third, then one-fourth.

How does the travel distance of the load change as you increase the number of pulleys from one to two, then three, then four?

Rotational inertia is the resistance to a change in rotational motion, which is similar to inertia which is a resistance to a change in velocity.

How is rotational inertia similar to inertia as studied in previous chapters?

ω =3 rotations per secondat

If a trapeze artist rotates once each second while sailing through the air and contracts to reduce her rotational inertia to one-third of what it was, how many rotations per second will result?

60%

If an input of 100 J in a pulley system increases the potential energy of a load by 60 J, what is the efficiency of the system?

K = 720 J

If the force of friction on the crate is a steady 70 N, find the KE gained by the crate.

four times

Suppose you are swirling a can around and suddenly decide to pull the rope in halfway; by what factor would the rotational speed of the can change?

Double

Suppose you are swirling a can around and suddenly decide to pull the rope in halfway; by what factor would the tangential speed of the can change?