Question 1

A 2 kg mass has 40 J of potential energy with respect to the ground.Approximately how high is it above the ground?

Accepted Answer

The potential energy (PE) is given by PE = mgh, where m is mass, g is the acceleration due to gravity (approximately 9.8 m/s²), and h is height. Solving for h: h = PE / (mg) = 40 J / (2 kg * 9.8 m/s²) ≈ 2 m.

Question 2

A ball is projected into the air with 100 J of kinetic energy which is transformed to gravitational 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, it has now transformed all of its kinetic energy into gravitational potential energy. However, due to air resistance, the ball loses some of its energy as it descends back to its original level. Therefore, the kinetic energy of the ball when it reaches its original level will be less than 100 J.

Question 3

A light aluminum ball and a heavy lead ball of the same size are allowed to roll down an incline.When they are halfway down the incline,they will have identical

Accepted Answer

The balls will have different kinetic energies, potential energies, momentum, and inertias due to their different masses, even though they are the same size.

Question 4

Two identical arrows,one with twice the kinetic energy of the other,are fired into a hay bale.The faster arrow will penetrate

Accepted Answer

The kinetic energy of an object is directly proportional to the square of its velocity. Therefore, if one arrow has twice the kinetic energy of the other, it must have a velocity that is the square root of 2 times greater. Since both arrows have the same mass, the faster arrow will have twice the momentum of the slower one. When the arrows hit the hay bale, they will experience an equal and opposite force that will slow them down. Because the faster arrow has more momentum, it will take longer to come to a stop and will penetrate the hay bale twice as far as the slower arrow.

Question 5

Using 1000 J of work,a toy elevator is raised from the ground floor to the second floor in 20 seconds.The power needed to do this job was

Accepted Answer

The answer of Using 1000 J of work,a toy elevator...

Question 6

Strictly speaking,more fuel is consumed by your car if an air conditioner,headlights,or even a radio is turned on.This statement is

Accepted Answer

When additional electrical components, such as the air conditioner, headlights, or radio, are used in a car, they require additional power from the engine, which ultimately increases fuel consumption. Therefore, the statement is true.

Question 7

It takes 40 J to push a large box 4 m across a floor.Assuming the push is in the same direction as the move,what is the magnitude of the force on the box?

Accepted Answer

The work done (W) is equal to the force (F) times the distance (d), W = F * d. Given W = 40 J and d = 4 m, we can solve for F: F = W/d = 40 J / 4 m = 10 N.

Question 8

A 2-kg mass is held 4 m above the ground.What is the approximate potential energy of the mass with respect to the ground?

Accepted Answer

The answer of A 2-kg mass is held 4 m...

Question 9

The ball rolling down an incline has its maximum potential energy at

Accepted Answer

The maximum potential energy of a ball on an incline is at the top because that is where the height is the greatest and height is directly proportional to potential energy. As the ball rolls down the incline, its potential energy decreases and its kinetic energy increases until it reaches the bottom where its potential energy is at a minimum and its kinetic energy is at a maximum.

Question 10

A ball rolling down an incline has its minimum speed

Accepted Answer

The minimum speed of the ball occurs near the top of the incline, where its potential energy is at its maximum and its kinetic energy is at its minimum. As the ball rolls down the incline, the potential energy decreases while the kinetic energy increases, until it reaches the bottom with its maximum kinetic energy and zero potential energy. The mass and size of the ball do not affect its minimum speed on the incline as long as there is no friction involved.

Question 11

A ball rolling down an incline has its maximum kinetic energy at

Accepted Answer

The ball rolling down an incline has its maximum potential energy at the top and the kinetic energy gradually increases as it rolls down. At the bottom, all the potential energy is converted into kinetic energy, hence the ball has its maximum kinetic energy at the bottom.

Question 12

A block of ice sliding down an incline has its maximum speed at

Accepted Answer

The block of ice will experience friction as it slides down the incline. As it moves downhill, the component of its weight parallel to the incline will accelerate the block of ice. The frictional force opposing the motion of the block will increase with increasing speed of the block. Therefore, the block will accelerate initially but will eventually reach a maximum speed when the frictional force is equal in magnitude to the component of its weight parallel to the incline. This occurs when the block reaches the bottom of the incline. Therefore, the maximum speed of the block will be at the bottom of the incline.

Question 13

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

Accepted Answer

Gravity does no work on the ball because the force of gravity acts vertically downward, which is perpendicular to the horizontal motion of the ball along the alley. Work is only done when the force has a component in the direction of the motion.

Question 14

A machine puts out 100 Watts of power for every 1000 Watts put into it.The efficiency of the machine is

Accepted Answer

The efficiency of a machine is calculated as (Output Power/Input Power) * 100%. Here, (100/1000) * 100% = 10%.

Question 15

One end of a long,uniform log is raised to shoulder level.Another identical log is raised at its center to the same level.Raising the second log requires about

Accepted Answer

Raising the second log requires twice as much work because the center of mass of the log is raised to a higher position compared to when one end is raised, effectively doubling the height through which the average weight is lifted.

Question 16

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

Accepted Answer

The kinetic energy (KE) of an object is proportional to the square of its velocity. If the faster car moves 4 times as fast as the slower car, then its velocity is 4^2 = 16 times greater than the slower car. Therefore, the faster car has 16 times the KE of the slower car.

Question 17

A pile driver hits the top of a telephone pole,driving it partway into the ground.The distance that the pole will sink into the ground depends on

Accepted Answer

The distance that the pole will sink into the ground depends on various factors such as the original height of the pile driver weight, the original potential energy of the pile driver weight, and the kinetic energy of the pile driver weight when it first contacted the pole. Therefore, any of the above choices can be a factor that affects the sinking of the pole into the ground.

Question 18

A TV set is pushed a distance of 2 m with a force of 20 N.How much work is done on the set?

Accepted Answer

Work is calculated by the formula: Work = Force x Distance. Here, Work = 20 N x 2 m = 40 J.

Question 19

What task requires the most work;lifting a 50-kg sack 2 meters or lifting a 25-kg sack 4 meters?

Accepted Answer

Both tasks require the same amount of work since work is calculated by multiplying force by distance. In this case, since the distance multiplied by the weight in both options is the same (100 J), the amount of work required is the same.

Question 20

Both a 50-kg sack is lifted 2 meters from the ground and a 25-kg sack is lifted 4 meters in the same time.The power expended in raising the 50-kg sack is

Accepted Answer

Power is defined as work done per unit time. Since both sacks are lifted in the same time, the work done on each sack is equal to its weight multiplied by the distance it is lifted.

For the 50-kg sack, the work done is:

W = Fd = mgd = (50 kg)(9.8 m/s^2)(2 m) = 980 J

For the 25-kg sack, the work done is:

W = Fd = mgd = (25 kg)(9.8 m/s^2)(4 m) = 980 J

Therefore, the work done on each sack is the same. Since the time taken to lift each sack is the same, the power expended in raising each sack must also be the same.

Therefore, the answer is C, the same.

Quiz 7: Energy