PS3-2 Kinetic & Potential Energy Quiz with Answer Explanations

A skier wants to go down a slope with the most kinetic energy possible. The best way to go faster is to start higher up. Why is this?

• Starting higher up will require less potential energy as the skier goes down.

• Starting higher up will start them with more kinetic energy.

• Starting higher up will start them with more potential energy, which will stay constant as the skiier goes down the slope.

• Starting higher up will start them with more potential energy, which is converted to kinetic energy later.

Answer explanation

Explanation:

The answer is "Starting higher up will start them with more potential energy, which is converted to kinetic energy later."

Potential Energy is “stored energy.” It is energy that is ready to be converted or released as another type of energy. We most often think of potential energy as gravitational potential energy. When objects are higher up, they are ready to fall back down. When you stretch an object and it has a tendency to return to its original shape, it is said to have elastic potential energy. Chemical potential energy is the stored energy in a substance’s chemical structure that can be released in a chemical reaction or as heat. 

Potential energy is greatest when the most energy is stored. This could be when an object reaches its highest point in the air before falling, a rollercoaster just before it drops, or when a rubber band is stretched as far back as possible before it snaps. Potential energy is then converted to kinetic energy.

 

What is the kinetic energy of a 4 kilogram book, falling at 5 meters per second? 

• 10 Joules

• 5 Joules

• 50 Joules

• 100 Joules

Answer explanation

The answer is 50 Joules. The equation for Kinetic Energy is: KE = 1/2 mv² and 1/2 of 4 x 5² = 50.

Kinetic energy has a direct relationship with mass, meaning that as mass increases so does the Kinetic Energy of an object. The same is true of velocity. However, mass and velocity are indirectly related. Objects with greater mass can have more kinetic energy even if they are moving more slowly, and objects moving at much greater speeds can have more kinetic energy even if they have less mass. We must consider both the speed and mass of objects when considering the outcomes of collisions.

You serve a volleyball with a mass of 2.1 kg. The ball leaves your hand with a speed of 30 m/s. What is the kinetic energy of the ball? 

• 9.45 Joules

• 1890 Joules

• 945 Joules

• 900 Joules

Answer explanation

The answer is 945 Joules. 1/2 of 2.1 x 30² = 945. 

The equation for Kinetic Energy is: KE = 1/2 mv². Kinetic energy has a direct relationship with mass, meaning that as mass increases so does the Kinetic Energy of an object. The same is true of velocity. However, mass and velocity are indirectly related. Objects with greater mass can have more kinetic energy even if they are moving more slowly, and objects moving at much greater speeds can have more kinetic energy even if they have less mass. We must consider both the speed and mass of objects when considering the outcomes of collisions.

Suppose you have a grocery cart. You are pushing it down the aisle and you continue to push with the same speed as you put more items in the cart. As you add more groceries to the cart, how will the Kinetic energy of the cart change?

Remains constant = doesn't change

• The kinetic energy of the cart will decrease because the mass is increasing while the speed remains constant.

• The kinetic energy of the cart will stay the same because the speed remains constant.

• The kinetic energy of the cart will increase because the mass is increasing while the speed remains constant.

• The kinetic energy of the cart will increase because more mass will need more force to push.

Answer explanation

The kinetic energy of the cart will increase because the mass is increasing while the speed remains constant.

The equation for Kinetic Energy is: KE = 1/2 mv². Kinetic energy has a direct relationship with mass, meaning that as mass increases so does the Kinetic Energy of an object. The same is true of velocity. However, mass and velocity are indirectly related. Objects with greater mass can have more kinetic energy even if they are moving more slowly, and objects moving at much greater speeds can have more kinetic energy even if they have less mass. We must consider both the speed and mass of objects when considering the outcomes of collisions.

True or false: If an object has more speed than something else, it definitely has more kinetic energy.

• True

• False

Answer explanation

The answer is false. An object with less speed and more mass could potentially have the same Kinetic energy.

The equation for Kinetic Energy is: KE = 1/2 mv^2. Kinetic energy has a direct relationship with mass, meaning that as mass increases so does the Kinetic Energy of an object. The same is true of velocity. However, mass and velocity are indirectly related. Objects with greater mass can have more kinetic energy even if they are moving more slowly, and objects moving at much greater speeds can have more kinetic energy even if they have less mass. We must consider both the speed and mass of objects when considering the outcomes of collisions.

If an object has 250 Joules of Kinetic energy and is traveling at a velocity of 5 meters per second, what is the objects mass?

• 2kg

• 20kg

• 25kg

• 1000kg

Answer explanation

The object has a mass of 20kg. Rearranging the formula for kinetic energy will allow you to work backwards. 250 Joules x 2 = 500 Joules. 500 Joules divided by the velocity squared (25) = 20 kg.

The equation for Kinetic Energy is: KE = 1/2 mv². Kinetic energy has a direct relationship with mass, meaning that as mass increases so does the Kinetic Energy of an object. The same is true of velocity. However, mass and velocity are indirectly related. Objects with greater mass can have more kinetic energy even if they are moving more slowly, and objects moving at much greater speeds can have more kinetic energy even if they have less mass. We must consider both the speed and mass of objects when considering the outcomes of collisions.

If a duck is flying at 3 meters per second, and has a mass of 2kg. What is the kinetic energy of the duck?

• 12 Joules

• 3 Joules

• 24 Joules

• 9 Joules

Answer explanation

The duck has a kinetic energy of 9 Joules. 

The equation for Kinetic Energy is: KE = 1/2 mv^2. Kinetic energy has a direct relationship with mass, meaning that as mass increases so does the Kinetic Energy of an object. The same is true of velocity. However, mass and velocity are indirectly related. Objects with greater mass can have more kinetic energy even if they are moving more slowly, and objects moving at much greater speeds can have more kinetic energy even if they have less mass. We must consider both the speed and mass of objects when considering the outcomes of collisions.

The equation for Kinetic Energy is: KE = 1/2 mv² . Based on this equation, what would have the greatest impact on the overall kinetic energy of a moving object?

• increasing the mass

• applying less force

• increasing the velocity

• applying more force

Answer explanation

The answer is increasing the velocity, because the velocity variable is squared and therefore an increase in velocity would have a greater impact on the overall kinetic energy.

The equation for Kinetic Energy is: KE = 1/2 mv². Kinetic energy has a direct relationship with mass, meaning that as mass increases so does the Kinetic Energy of an object. The same is true of velocity. However, mass and velocity are indirectly related. Objects with greater mass can have more kinetic energy even if they are moving more slowly, and objects moving at much greater speeds can have more kinetic energy even if they have less mass. We must consider both the speed and mass of objects when considering the outcomes of collisions.

If all of these objects have the same mass, which of these sets of objects would feel greater gravitational potential pull?

• they have the same gravitational energy

• the objects that are 100 meters apart

• it would depend on the temperature of the objects

• the objects that are 10 meters apart

Answer explanation

Two objects that are closer together have a stronger gravitational pull because the force of gravity between two objects depends on both their masses and the distance between them. According to the law of universal gravitation, the force of gravity increases as the distance between objects decreases. This means the closer two objects are, the stronger the gravitational attraction between them.

Which of these two objects would have a greater gravitational pull?

• not enough information

• they have the same gravitational energy

• the 5kg object

• the 100kg object

Answer explanation

The answer is "the 100 kg object" because it has a greater mass. Reminder that the size of the object does not affect the gravitational energy.

Gravitational energy exists between all objects. We rarely talk about the gravitational energy that exists between objects here on Earth because the pull is so weak. We consider the effect of gravity more often when we talk about planets, stars, and galaxies because they are more massive and have much stronger forces of gravity at work. 

The gravitational potential energy of an object depends on the mass of objects, and how far away they are from each other. More massive objects have more gravitational pull. (Remember that just because something is bigger, doesn’t mean it has more mass!) Objects that are closer together have more gravitational pull. 

Weight is a measure of the effect of gravity on an object, and can change depending on where we are. Our mass never changes but we weigh less on the moon because there is less gravitational energy between us and the moon. The moon has less gravitational energy than Earth because it is less massive.