Question 1

A mass hangs from a spring that is fixed to the ceiling. The mass is now pulled down and released so the mass oscillates up and down. Which of the following statements is true?

Accepted Answer

None of the statements are true. The kinetic energy of the oscillating mass is not constant as it varies with the position of the mass. Adding mass to the spring will actually make it oscillate slower, not faster. The restoring force of the spring is not equal to the weight of the mass; it varies with displacement. The gravitational force on the mass is constant and does not oscillate.

Question 2

When work is done by a force on an object, then which of the following is true?

Accepted Answer

According to the work-energy principle, the work done on an object is equal to the change in its kinetic energy plus any energy that appears as heat, light, or sound. Therefore, choice C is true. The other choices are not necessarily true in all cases. For example, the force could be applied perpendicular to the motion of the object, in which case the speed would not change (choice A). The object could also be stationary or moving with a constant speed, in which case there would be no change in kinetic energy (choice C). The object could also move horizontally and not change its height above the ground (choice D). Finally, the statement in choice E is not true, since the force could in fact take energy away from the object if it is a dissipative force, such as friction.

Question 3

For a 0.1-kg frog to jump to a height of 1.0 meter requires an energy of about

Accepted Answer

The energy required to lift an object of mass m to a height h is given by the formula E = mgh, where g is the acceleration due to gravity. Plugging in the given values, we get:
E = (0.1 kg)(9.8 m/s^2)(1.0 m) = 0.98 Joule
Therefore, the closest answer choice is B) 1.0 Joule.

Question 4

Which of the following is possessed by a moving object, but not by a stationary object?

Accepted Answer

Kinetic energy is possessed by a moving object due to its motion, whereas a stationary object does not possess any kinetic energy. Mass and inertia are properties of an object that exist regardless of motion, and energy can exist in various forms, including potential energy, which can be possessed by both stationary and moving objects.

Question 5

A child riding on a swing rises to a height 1.0 m above the lowest point. Another child of equal mass whose speed at the lowest point is twice as great will rise

Accepted Answer

The energy in a swing is a combination of kinetic energy at the lowest point and potential energy at the highest point. When the speed at the lowest point is doubled, the kinetic energy becomes four times greater (since kinetic energy is proportional to the square of the velocity), allowing the swing to rise four times as high to convert this increased kinetic energy into potential energy.

Question 6

Which of the following is not an energy unit?

Accepted Answer

Watt is a unit of power, not energy.

Question 7

Virgil rides a skateboard (combined mass 100 kg) at 4 m/s, and Jill rides a bicycle (combined mass 64 kg) at 5 m/s.

Accepted Answer

The answer of Virgil rides a skateboard (combined mass 100...

Question 8

Jim exerts a force of 500 N against a 100-kg desk that does not move. Virgil exerts a force of 400 N against a 60-kg desk that moves 2 m in the direction of the push. Mik exerts a force of 200 N against a 50-kg desk that moves 5 m in the direction of the push. The most work is done by

Accepted Answer

The amount of work done is determined by the formula W = Fd (work equals force times distance).

Jim exerts a force of 500 N, but since the desk does not move, no work is done (d = 0).

Virgil exerts a force of 400 N over a distance of 2 m, so the work done is W = (400 N) x (2 m) = 800 J.

Mik exerts a force of 200 N over a distance of 5 m, so the work done is W = (200 N) x (5 m) = 1000 J.

Therefore, Mik does the most work.

Question 9

If work was done on an object, the object must have

Accepted Answer

Work is defined as the force applied on an object causing it to move in the direction of the force. Therefore, if work is done, the object must have changed its position.

Question 10

Suppose you climb the stairs of an eight-story building, about 24 m high, and your mass is 70 kg. The gravitational potential energy you gain is about

Accepted Answer

The gravitational potential energy gained by the person is given by the formula:
GPE = mgh
where m is the mass of the person (70 kg), g is the acceleration due to gravity (9.8 m/s^2), and h is the height climbed (24 m).
GPE = 70 x 9.8 x 24
GPE = 16,464 Joule (approx.)
Therefore, the correct answer is C) 16,500 Joule.

Question 11

A brick slides across a horizontal rough surface and eventually comes to a stop. What happened to the kinetic energy of the brick?

Accepted Answer

When the brick slides across a rough surface, the kinetic energy is converted to other energy forms, mostly heat. This is due to the frictional force between the brick and the surface which opposes the motion of the brick and causes it to lose its kinetic energy. Therefore, option B is the correct answer. Option A is incorrect as the kinetic energy cannot be transformed into potential energy unless there is some potential energy associated with the system. Option C is incorrect as friction does not have potential energy. Option D is incorrect as the law of conservation of energy states that energy cannot be destroyed, only converted from one form to another.

Question 12

The power of an engine is a measure of

Accepted Answer

The power of an engine is a measure of the rate at which it can perform work, or the amount of work done per unit of time.

Question 13

Initially, a blue automobile has twice the kinetic energy that a red automobile has. Both are braked to a stop; both have the same amount of braking force. The red auto will stop in ____________________ as the blue auto.

Accepted Answer

Since kinetic energy is directly proportional to the square of the velocity and the work done to stop the car (which is equal to the kinetic energy due to the work-energy principle) is the same for both cars, the distance covered during braking (work done against friction) is directly proportional to the kinetic energy. If the blue car has twice the kinetic energy, it will require twice the work to stop, implying it will stop in twice the distance. Thus, the red car will stop in half the distance compared to the blue car.

Question 14

A box is moved 10 m across by a floor a force of 25 N acting along the direction of motion. The work done by the force is

Accepted Answer

Work done = force x distance moved in the direction of force
In this case, force = 25 N and distance moved = 10 m
Therefore, work done = 25 N x 10 m = 250 J

Question 15

A block sits on a slight incline, held at rest by the frictional force between the block and the incline. Which of the following statements is true?

Accepted Answer

The frictional force indeed performs no work on the block because there is no displacement. Work is defined as the force applied over a distance, and since the block does not move, the distance is zero, making the work done by friction zero as well.

Question 16

An object with a kinetic energy of 40 J is stopped in a distance of 0.01 m. The average force that stops the object is

Accepted Answer

The work done to stop the object is equal to its initial kinetic energy, which is 40 J. The work done by the stopping force can also be calculated using the formula Work = Force x Distance. Setting these equal gives us 40 J = Force x 0.01 m, solving for Force gives us 4000 N.

Question 17

A 3.0-kg cat runs to the left at 10 m/s and a 10-kg dog runs to the right at 4.0 m/s. The total kinetic energy is

Accepted Answer

The total kinetic energy is calculated by summing the kinetic energies of both the cat and the dog. The kinetic energy (KE) is given by the formula KE = 0.5 * m * v^2. For the cat: KE_cat = 0.5 * 3.0 kg * (10 m/s)^2 = 150 Joules. For the dog: KE_dog = 0.5 * 10 kg * (4.0 m/s)^2 = 80 Joules. The total kinetic energy is 150 Joules + 80 Joules = 230 Joules.

Question 18

Which has the greater kinetic energy-a 1-ton car moving at 30 m/s or a half-ton car moving at 60 m/s?

Accepted Answer

The kinetic energy (KE) is given by the formula KE = 1/2 mv^2, where m is the mass and v is the velocity. For the 1-ton car (1000 kg) moving at 30 m/s, KE = 1/2 * 1000 * 30^2 = 450,000 Joules. For the half-ton car (500 kg) moving at 60 m/s, KE = 1/2 * 500 * 60^2 = 900,000 Joules. Therefore, the half-ton car has greater kinetic energy.

Question 19

A quarterback of mass 85 kg is running at 10 m/s. Also, a tackle of mass 100 kg is running at 9 m/s.

Accepted Answer

The kinetic energy of an object is given by the formula KE = 0.5*m*v^2, where m is the mass of the object and v is its velocity. 
Plugging in the values given for the quarterback: 
KE = 0.5 * 85 kg * (10 m/s)^2 = 4,250 J 
Plugging in the values given for the tackle: 
KE = 0.5 * 100 kg * (9 m/s)^2 = 4,050 J 
Since the velocity of the quarterback is higher than the tackle, the quarterback has a greater kinetic energy. Therefore, the answer is choice C.

Question 20

A 20 N ball and a 40 N ball are dropped at the same time from a height of 10 meters. Air resistance is negligible. Which of the following statements is accurate?

Accepted Answer

Both balls have the same acceleration due to gravity, so A is incorrect. The heavy ball has a greater force acting on it due to its greater weight, but this does not necessarily mean it has a greater acceleration or falls faster, so B and D are incorrect. Both balls are dropped from the same height and experience the same change in potential energy, so they have the same amount of work done on them by gravity. However, since the heavy ball has a greater weight, it experiences a greater force and therefore a greater amount of work is done on it by gravity, so C is accurate – gravity does more work on the heavy ball than on the light ball. Both balls hit the ground at the same time because they have the same acceleration due to gravity.

Quiz 6: Energy and Oscillations