Question 1

If you do work on an object in half the time,your power output is

Accepted Answer

Power is the rate at which work is done, measured in watts (W). Power (P) = work (W) / time (t). If you do the same amount of work in half the time, your power output has doubled because you are doing the work in less time. Therefore, the correct answer is option C) twice.

Question 2

A car moves 4 times as fast as another identical car.Compared with the slower car,the faster car has

Accepted Answer

Kinetic energy is proportional to the square of velocity. Since the faster car moves 4 times as fast as the slower car, its kinetic energy is (4)^2 = 16 times as much. Therefore, the faster car has 16 times the kinetic energy of the slower car. Thus, choice D is correct.

Question 3

You do work on a cart loaded with groceries.If you do this work in one-third the usual time,you expend

Accepted Answer

Power is defined as work done per unit time. As the work done (moving the cart loaded with groceries) is the same, doing it in one-third the usual time means expending three times the usual power. Therefore, the correct answer is (C) three times the usual power.

Question 4

If you exert 100 J to lift a box in 50 s your power output is

Accepted Answer

Power is calculated as work done divided by time. Here, power = 100 J / 50 s = 2 W.

Question 5

If you exert 6 N across a distance of 2 m in 3 s you'll deliver a power of

Accepted Answer

The formula for power is P = W/t where W is the work done and t is the time taken. The work done is calculated as W = F*d, where F is the force applied and d is the distance covered.

In this case, the force applied is 6 N and the distance covered is 2 m. So, the work done is W = 6 N * 2 m = 12 J.

The time taken is 3 s. So, the power delivered is calculated as P = W/t = 12 J / 3 s = 4 W.

Therefore, the best choice is C.

Question 6

Power is defined as the

Accepted Answer

Power is defined as the rate at which work is done, which is the work done divided by the time taken to do the work. Therefore, the best choice is D.

Question 7

Which has the greater kinetic energy?

Accepted Answer

Kinetic energy is given by 1/2 mv^2 where m is the mass of the object and v is its velocity. Therefore, the kinetic energy of a car is directly proportional to the square of its velocity and mass. In option B, the car is half the mass, but it is traveling at twice the speed of the car in option A. Thus, its kinetic energy would be (1/2)(1/2)m(2v)^2 = 2mv^2 which is greater than the kinetic energy of the car in option A. Therefore, the correct answer is B.

Question 8

No work is done by gravity on a bowling ball that rolls along a bowling alley because

Accepted Answer

The force of gravity acts downward, while the motion of the ball is horizontal. Since work is calculated as the force applied in the direction of motion times the distance moved, and the angle between the force of gravity and the direction of motion is 90 degrees, no work is done by gravity in this scenario.

Question 9

A 50-kg sack is lifted 2 m in the same time as a 25-kg sack is lifted 4 m.The power expended in raising the 50-kg sack compared to the power used to lift the 25-kg sack is

Accepted Answer

The work done on both sacks is the same (force x distance), as they both were lifted the same amount of work: (50 kg x 9.8 m/s^2 x 2 m) = (25 kg x 9.8 m/s^2 x 4 m) = 980 J.

Power is work done per unit time, and since the work done is the same but the distance covered and time are different for both sacks, the power expended in lifting them should be the same. Therefore, the power expended in raising the 50-kg sack is the same as the power required to lift the 25-kg sack, and the answer is C - the same.

Question 10

The power expended for a barbell raised 2.0 m in 2 s is

Accepted Answer

To calculate power, we need both the force applied to the barbell (or its weight, which depends on its mass and gravity) and the distance over which it is moved. The time over which the action occurs is given, but without the mass of the barbell or a force value, we cannot calculate the work done or the power expended.

Question 11

When a bus brakes to a stop its kinetic energy transforms to

Accepted Answer

When a bus brakes to a stop, its kinetic energy (energy of motion) is transformed into heat due to friction between the brake pads and the wheels, as well as between the tires and the road.

Question 12

A shopping cart moves with a kinetic energy of 40 J.If it moves at twice the speed,its kinetic energy is

Accepted Answer

The kinetic energy of a moving object is directly proportional to the square of its velocity. Therefore, if the velocity of the shopping cart is doubled, its kinetic energy will be four times greater.

Mathematically:

K = (1/2)mv^2

If v is doubled, then:

K' = (1/2)m(2v)^2 = 4(1/2)mv^2 = 4K

Therefore, if the initial kinetic energy is 40 J, then doubling the velocity will result in a kinetic energy of 160 J.

Question 13

A car that travels twice as fast as another car when braking to a stop will skid

Accepted Answer

The distance skidded is directly proportional to the square of the velocity at the start of braking. Therefore, if one car is traveling twice as fast as the other, its initial speed will be quadruple that of the slower car. Thus, when it brakes to a stop, it will skid four times as far as the slower car. Therefore, option B is correct.

Question 14

A car moving at 50 km/h skids 20 m with locked brakes.How far will it skid if its initial speed is 150 km/h?

Accepted Answer

The distance skidded is directly proportional to the square of the initial speed. Therefore, if the initial speed is tripled, the distance skidded will be nine times as much. So, 20 m skidded at 50 km/h means 180 m will be skidded at 150 km/h.

Question 15

Which has greater kinetic energy: a car traveling at 30 km/h or another car of half the mass traveling at 60 km/h?

Accepted Answer

Kinetic energy is directly proportional to mass and also to the square of speed. Therefore, the 60-km/h car has greater kinetic energy as it has a higher speed and the same mass as the other car.

Question 16

A ball is projected into the air with 900 J of kinetic energy that is transformed to potential energy at the top of its trajectory.When it returns to its original level after encountering air resistance,its kinetic energy is

Accepted Answer

When the ball reaches the top of its trajectory, all its kinetic energy has transformed into potential energy. However, when it returns to its original level, it encounters air resistance which will dissipate some of its energy as heat. Therefore, its kinetic energy will be less than 900 J.

Question 17

Which requires more work: lifting a 50-kg sack vertically 2 m or lifting a 25-kg sack vertically 4 m?

Accepted Answer

Work done is defined as the force applied multiplied by the distance over which it is applied. In both cases, the force required would be the same (assuming the same acceleration due to gravity). Therefore, the work done would depend only on the vertical distance over which the sack is lifted. It can be observed that in the first case, the 50-kg sack is lifted only half the distance as compared to the second case, where the 25-kg sack is lifted. Hence, both cases require the same amount of work.

Question 18

A cat and a mouse run along a road with the same kinetic energy.The faster runner is the

Accepted Answer

The mouse is faster because it has less mass than the cat. With the same kinetic energy, the mouse must have a higher velocity to compensate for its lower mass.

Question 19

Using 1000 J of work,a toy elevator is raised from the ground floor to the second floor in 20 s.How much power does the elevator use?

Accepted Answer

Power is defined as work done per unit time. Here, 1000 J of work is done in 20 s, so the power used is 1000 J / 20 s = 50 W.

Question 20

The massive ram of a pile driver falling from rest strikes a pile with a speed that depends on the

Accepted Answer

The final speed of the ram will depend on the initial potential energy of the ram, which is determined by the height from which it falls, as well as the distance it falls. Therefore, all of the choices affect the speed of the ram.

Quiz 3: Momentum and Energy