Question 1

Consider a situation where you exert a force F on a crate of mass m, moving it at a speed v a distance d across a floor in a time interval t.
-The linear momentum of the crate is Fv.

Accepted Answer

The linear momentum of the crate is given by p = mv, not Fv. The force applied by you results in an acceleration, which in turn changes the velocity of the crate. This change in velocity over time is what results in a change in momentum.

Question 2

Consider a situation where you exert a force F on a crate of mass m, moving it at a speed v a distance d across a floor in a time interval t.
-The work you do on the crate is Fv.

Accepted Answer

The work done on the crate is given by the formula W = Fd, where d is the distance moved by the crate in the direction of the force. In this case, the distance moved is d = vt. Therefore, the work done is W = Fvt.

Question 3

Consider a situation where you exert a force F on a crate of mass m, moving it at a speed v a distance d across a floor in a time interval t.
-The power you supply to the crate is Fd/t.

Accepted Answer

According to the formula for power, P = W/t = (Fd cosθ)/t, where θ is the angle between the force and displacement vectors. In this case, since the force is applied in the direction of motion (i.e. θ = 0), we have P = Fd/t. Therefore, the statement is true.

Question 4

If the velocity of an aircraft is doubled,the kinetic energy of the aircraft is also doubled.

Accepted Answer

The kinetic energy of an aircraft is proportional to the square of its velocity. Therefore, if the velocity is doubled, the kinetic energy is actually quadrupled (i.e., multiplied by 2 raised to the power of 2).

Question 5

A watt is equal to 746 horsepower.

Accepted Answer

One horsepower is equal to approximately 0.746 watts. Therefore, one watt is equal to approximately 0.00134 horsepower.

Question 6

Consider a situation where you carry a 20-N box up a flight of stairs, raising its elevation by 5 m.
-When the box hits the floor its kinetic energy is converted into internal energy.

Accepted Answer

When the box hits the floor, its kinetic energy is converted into internal energy, causing the floor and the box to heat up.

Question 7

A spacecraft can gain energy by passing near a planet.

Accepted Answer

This is true. A spacecraft can use a planet's gravity to slingshot around the planet and gain energy. This technique is often used for interplanetary missions to save fuel and increase speed.

Question 8

Consider a situation where you exert a force F on a crate of mass m, moving it at a speed v a distance d across a floor in a time interval t. -The kinetic energy of the crate is 1/2 mv².

Accepted Answer

The kinetic energy of an object is given by the formula KE = 1/2 mv², where m is the mass and v is the velocity of the object.

Question 9

When more people ride upward in an elevator,more power is required.

Accepted Answer

When more people ride upward in an elevator, the weight of the elevator increases, and thus more power is required to lift it. This is due to the increase in the force of gravity acting on the elevator, which is proportional to the weight of the elevator and its contents.

Question 10

A person runs up a long flight of stairs in 10 seconds.If the person's weight is 600 N and the vertical height of the stairs is 20 meters,the person's power output is 1,200 W.

Accepted Answer

Power output = (Work done)/(Time taken)
Work done = force x distance = 600 N x 20 m = 12,000 J
Time taken = 10 s
Power output = 12,000 J/10 s = 1,200 W

Question 11

Consider a situation where you carry a 20-N box up a flight of stairs, raising its elevation by 5 m.
-You drop the box.As it falls to its original level,its kinetic energy is 100 J.

Accepted Answer

The box's potential energy at the top is converted to kinetic energy as it falls. The potential energy at 5 m is 20 N * 5 m = 100 J, which matches the kinetic energy when it reaches the original level.

Question 12

Consider a situation where you carry a 20-N box up a flight of stairs, raising its elevation by 5 m.
-The work you do is 4 J.

Accepted Answer

The work done in lifting a box to a height h is given by W = mgh where m is the mass of the box, g is the acceleration due to gravity, and h is the height. Therefore, W = (20 N) * (9.81 m/s^2) * (5 m) = 981 J. Since the given work is only 4 J, it is not possible to raise the box to a height of 5 m with that amount of work.

Question 13

Consider a situation where you carry a 20-N box up a flight of stairs, raising its elevation by 5 m.
-The increase of potential energy of the box is 100 J.

Accepted Answer

The formula for potential energy (PE) is PE = mgh, where m is the mass of the object (in kilograms), g is the acceleration due to gravity (9.8 m/s^2), and h is the height or elevation (in meters). In this case, the potential energy increase is calculated as PE = 20 * 9.8 * 5 = 980 J. Therefore, the answer is A, as the increase of potential energy is indeed 980 J, not 100 J.

Question 14

The collision between two cars in an accident is an inelastic collision.

Accepted Answer

The answer of The collision between two cars in an...

Question 15

When a car comes to a stop its kinetic energy is converted to internal energy in its brakes,heating them up.

Accepted Answer

When a car comes to a stop, its kinetic energy is transformed into thermal energy due to friction between the brakes and the wheels. This thermal energy increases the internal energy of the brakes, causing them to heat up. Therefore, option A is true.

Question 16

The measure of a body's resistance to being rotated is its angular momentum.

Accepted Answer

The measure of a body's resistance to being rotated is its moment of inertia. Angular momentum is the product of moment of inertia and angular velocity.

Question 17

Consider a situation where you exert a force F on a crate of mass m, moving it at a speed v a distance d across a floor in a time interval t.
-The potential energy of the crate is mgd.

Accepted Answer

The potential energy of the crate is given by P.E. = mgh, where h is the height from a reference point. In this scenario, the force F is used to move the crate horizontally, so there is no change in height and therefore no potential energy gained or lost.

Question 18

A rocket can never go faster than the speed of its exhaust.

Accepted Answer

This statement is false. According to Newton's Third Law of Motion, for every action there is an equal and opposite reaction. Therefore, the rocket's motion forward is related to the action of the exhaust pushing backwards. However, the speed of the rocket can be increased by continuously ejecting more exhaust at higher speeds, as is done with multi-stage rockets.

Question 19

A 2 kg car moving towards the right at 4 m/s collides head on with an 8 kg car moving towards the left at 2 m/s,and they stick together.After the collision,the velocity of the combined bodies is 0.8 m/s pointing towards the left.

Accepted Answer

We can use the law of conservation of momentum to solve this problem. The total momentum before the collision is:

P_initial = (2 kg)(4 m/s) - (8 kg)(2 m/s)
P_initial = 0 kg m/s (because one car is moving to the right and the other to the left)

After the collision, the two cars stick together and move with a velocity of 0.8 m/s towards the left. The total momentum after the collision is:

P_final = (10 kg)(-0.8 m/s)
P_final = -8 kg m/s

Since momentum is conserved, we have:

P_initial = P_final
0 kg m/s = -8 kg m/s

This means that the answer is true, and the combined bodies move towards the left after the collision.

Question 20

You carry a 20-N box 5 m horizontally across a room.The work you do is 100 N-m.

Accepted Answer

The work done is found by multiplying the force applied by the distance moved in the direction of the force (W = Fd). Since the force applied is horizontal and the box is being moved horizontally, the angle between the force and displacement is 0 degrees. Therefore, the work done is:

W = Fd = (20 N)(5 m)cos(0) = 100 J

The unit for work is Joules (J), not Newton-meters (N-m). So, the given work of 100 N-m is actually equivalent to 100 J. Therefore, the statement is false.

Quiz 3: Energy and Conservation Laws

Consider a situation where you exert a force F on a crate of mass m, moving it at a speed v a distance d across a floor in a time interval t. -The linear momentum of the crate is Fv.

Consider a situation where you exert a force F on a crate of mass m, moving it at a speed v a distance d across a floor in a time interval t. -The work you do on the crate is Fv.

Consider a situation where you exert a force F on a crate of mass m, moving it at a speed v a distance d across a floor in a time interval t. -The power you supply to the crate is Fd/t.

If the velocity of an aircraft is doubled,the kinetic energy of the aircraft is also doubled.

A watt is equal to 746 horsepower.

Consider a situation where you carry a 20-N box up a flight of stairs, raising its elevation by 5 m. -When the box hits the floor its kinetic energy is converted into internal energy.

A spacecraft can gain energy by passing near a planet.

Consider a situation where you exert a force F on a crate of mass m, moving it at a speed v a distance d across a floor in a time interval t. -The kinetic energy of the crate is 1/2 mv2.

When more people ride upward in an elevator,more power is required.

A person runs up a long flight of stairs in 10 seconds.If the person's weight is 600 N and the vertical height of the stairs is 20 meters,the person's power output is 1,200 W.

Consider a situation where you carry a 20-N box up a flight of stairs, raising its elevation by 5 m. -You drop the box.As it falls to its original level,its kinetic energy is 100 J.

Consider a situation where you carry a 20-N box up a flight of stairs, raising its elevation by 5 m. -The work you do is 4 J.

Consider a situation where you carry a 20-N box up a flight of stairs, raising its elevation by 5 m. -The increase of potential energy of the box is 100 J.