Question 1

The main energy transformation that occurs while an electric blender is mixing your orange juice is

Accepted Answer

The electric energy from the blender is transformed into kinetic energy of the blades, which then mix the orange juice.

Question 2

The figure above shows a marble rolling freely back and forth along a curved track. The track is positioned vertically. Assuming no friction and no air resistance, the total energy of the marble

Accepted Answer

In the absence of friction and air resistance, the total mechanical energy (potential + kinetic) of the marble remains constant due to the conservation of energy.

Question 3

A particular lightbulb produces 8 J of thermal energy while producing 2 J of radiant energy, and this is its entire energy output during this time. How energy- efficient is this bulb [as a producer of light]?

Accepted Answer

The energy efficiency of the bulb as a producer of light is calculated by dividing the radiant energy output (2 J) by the total energy output (8 J + 2 J = 10 J), which gives 0.2 or 20%.

Question 4

Which of these energy transformations best describes the overall operation of a hydroelectric power plant?

Accepted Answer

In a hydroelectric power plant, gravitational potential energy of water is converted into electrical energy (electromagnetic energy) as water flows down and turns turbines connected to generators.

Question 5

Regarding the validity of the law of conservation of energy,

Accepted Answer

The law of conservation of energy is a fundamental principle of physics that holds true in all known situations, including those beyond the scope of Newtonian physics, such as in quantum mechanics and relativity.

Question 6

You throw a baseball horizontally, and Jill catches it. Neglect air resistance. The energy transformation that occurs during the throw [while the ball is in your hand] is

Accepted Answer

The energy transformation during the throw involves converting the chemical energy in your muscles into kinetic energy of the baseball.

Question 7

A gas can containing a gallon of gasoline is stored in a basement. This gasoline contains

Accepted Answer

Gasoline contains chemical energy that can be converted into other forms of energy, such as mechanical energy, when used as fuel.

Question 8

The power of American automobiles is usually rated in "horsepower." What other units could be used?

Accepted Answer

Horsepower is a unit of power, and watts are also a unit of power. Joules and Calories are units of energy, not power.

Question 9

What form or forms of energy does a falling elastic ball have when it is at its most- squeezed position on the floor, before it begins to rebound [see figure above]?

Accepted Answer

At its most-squeezed position, the ball has converted its kinetic and gravitational potential energy into elastic potential energy.

Question 10

A block of ice slides freely [no air resistance, no friction] down a slippery slope. The block starts from rest at the top of the slope, where it has a vertical height of 4 m above the bottom of the slope and where it has a gravitational energy of 1000 J. At a quarter of the way down the slope, the block's gravitational energy is

Accepted Answer

The gravitational potential energy decreases linearly with height. At a quarter of the way down, the block has descended 1 m, leaving it 3 m above the bottom. Thus, it retains 3/4 of its initial gravitational energy: 3/4 * 1000 J = 750 J.

Question 11

Suppose you slowly, and at constant speed, lift a book weighing 12 N from the floor to a shelf 2 m above the floor. Neglect air resistance. The work done by you on the book is

Accepted Answer

The work done is calculated by the formula: Work = Force x Distance. Here, the force is 12 N and the distance is 2 m, so the work done is 12 N x 2 m = 24 joules.

Question 12

In order to quadruple an object's kinetic energy, we must

Accepted Answer

Doubling the speed of an object results in quadrupling its kinetic energy because kinetic energy is proportional to the square of the speed (KE = 1/2 mv^2).

Question 13

There are no known exceptions to

Accepted Answer

The law of conservation of energy is a fundamental principle of physics that states energy cannot be created or destroyed, only transformed. There are no known exceptions to this law. Newton's laws of motion, however, have limitations at relativistic speeds and quantum scales.

Question 14

One situation in which the law of conservation of energy is violated is

Accepted Answer

The law of conservation of energy is a fundamental principle of physics that states energy cannot be created or destroyed, only transformed. No violations of this law have been observed, even in extreme conditions like near black holes or at atomic scales.

Question 15

Under what condition can a force act on an object and yet do no work on that object?

Accepted Answer

Work is defined as the force applied on an object times the distance the object moves in the direction of the force. If the object does not move, the distance is zero, and thus no work is done.

Question 16

Elizabeth lifts a 10 N book from the floor to the table, a height of 2 m. How much work does Elizabeth do?

Accepted Answer

Work is calculated as the force applied times the distance moved in the direction of the force. Here, work = 10 N * 2 m = 20 joules.

Question 17

Which of the following energy transformations represents the operation of a wind turbine [a device that uses the wind as an energy resource]?

Accepted Answer

Kinetic energy of the wind is converted into electrical energy by a wind turbine.

Question 18

A block of ice slides freely [no air resistance, no friction] down a slippery slope. The block starts from rest at the top of the slope, where it has a vertical height of 4 m above the bottom of the slope and where it has a gravitational energy of 1000 J. The block's total energy a quarter of the way down the slope [at a height of 3 m] is

Accepted Answer

The total mechanical energy of the block is conserved since there is no friction or air resistance. Therefore, the total energy remains 1000 J throughout the motion.

Question 19

A physics professor pushes against a stationary wall, "working" up a sweat. Is he doing any actual physical work on the wall?

Accepted Answer

In physics, work is defined as force applied over a distance. Since the wall is not moving, no work is done on it.

Question 20

You push your physics book across your desk, leaving the book at rest on the desk at the end of the process. Which of the following best represents the overall energy conversion during this process?

Accepted Answer

The energy conversion involves the chemical energy from your muscles being converted into thermal energy due to friction between the book and the desk.

Quiz 6: Conservation of Energy: You Cant Get Ahead