6B Unit 3 Test Review

Which is a good description of kinetic energy?

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    stored energy

• conserved energy

• energy from the sun

• energy of motion

Answer explanation

Kinetic energy is defined as the energy of motion. It is the energy an object possesses due to its movement, making 'energy of motion' the correct description. The other options refer to different energy concepts.

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A person throws a ball up into the air. At which point in its path will the ball have the greatest potential energy?

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    when the ball reaches its highest point

• when the ball leaves the person’s hand

• when the ball hits the ground

• when the ball is still rising

Answer explanation

The ball has the greatest potential energy when it reaches its highest point because potential energy is directly related to height. At this point, the ball's speed is zero, and all its energy is potential.

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NGSS.MS-PS2-4

A player throws a baseball straight up so that the ball rises and then falls back down to the player’s hand. Which of the following changes will occur if the player throws the ball up higher and then catches it?

• The ball will have greater potential energy at the top of its path.

• The ball will have greater kinetic energy at the top of its path.

• The ball will have more potential energy than kinetic energy when it is half-way back down to the player’s hand.

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    The ball will have more kinetic energy than potential energy when it is half-way back down to the player’s hand.

Answer explanation

When the player throws the ball higher, it gains more height, resulting in greater potential energy at the top of its path due to the increased height. Kinetic energy is highest just before it reaches the top.

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Two students drop an object into sand from a height of 1.5 meters. They record the depth of the hole made in the sand by each student’s object. What is the most likely explanation for the results?

Responses

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    Maddie’s object has a smaller width.

• Naveed’s object had greater kinetic energy.

• Naveed’s object has less mass.

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    Maddie’s object had a faster drop speed.

Answer explanation

Naveed’s object had greater kinetic energy, likely due to a greater mass or drop speed, resulting in a deeper hole in the sand compared to Maddie’s object.

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A student wants to determine the effect of mass on kinetic energy. She will drop two balls of the same size into a pool of water. Which investigation method should the student use?

• She should drop two balls with different masses from different heights.

• She should drop two balls of the same mass from the same height.

• She should drop two balls of the same mass from different heights.

• She should drop two balls with different masses from the same height.

Answer explanation

To determine the effect of mass on kinetic energy, the student should drop two balls with different masses from the same height. This ensures that the only variable affecting kinetic energy is mass, allowing for a clear comparison.

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Which falling object will result in the least kinetic energy when it collides with the ground?

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    100 grams of water falling at 10 m/s

• 10 grams of dirt falling at 2 m/s

• 10 grams of water falling at 1 m/s

• 100 grams of dirt falling at 15 m/s

Answer explanation

Kinetic energy is calculated as KE = 0.5 * mass * velocity^2. The 10 grams of water at 1 m/s has the least kinetic energy (0.5 * 0.01 * 1^2 = 0.005 J) compared to the other options, making it the correct choice.

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This image of a roller coaster is designed to show important information about potential and kinetic energy. One of these labeled pieces of information is incorrect. Which information is wrong, and why?

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    The spot with the “maximum kinetic energy” should be on the lowest point of the roller coaster, at the far left side on the bottom.

• The spot marked “maximum gravitational potential energy” should be on the lowest point of the roller coaster, at the far left side on the bottom.

• The roller coaster would only have potential energy at the point labeled “gravitational potential energy and kinetic energy.”

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    The roller coaster would only have kinetic energy at the point labeled “gravitational potential energy and kinetic energy.”

Answer explanation

The spot with 'maximum kinetic energy' should be at the lowest point of the roller coaster, where the speed is highest. At this point, gravitational potential energy is converted to kinetic energy, making it incorrect to label it otherwise.

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Which situation describes a non-contact force changing the speed of an object?

• a bicycle accelerating as the rider pedals more quickly

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    a drawer opening when a user pulls the handle

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    a gust of wind blowing a leaf away

• • 
    

    a ball accelerating as it rolls down a hill

Answer explanation

A ball accelerating as it rolls down a hill is an example of a non-contact force (gravity) changing the speed of the ball. The other options involve contact forces or do not describe a change in speed due to a non-contact force.

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In which situation would the momentum of a moving object increase?

• A force acting in the direction opposite the object’s motion is removed from the object.

• Two forces of equal magnitude act on the object in opposite directions.

• A new force acts on the object, opposing the object’s motion.

• A force acting in the direction of the object’s motion is removed from the object.

Answer explanation

Removing a force acting opposite to the object's motion reduces the opposing effect, allowing the object's momentum to increase. This is why the correct choice is the first option.

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You and a friend are throwing a ball back and forth to each other. What must be true about the ball in order for its momentum to change?

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    All forces on it must have equal strength.

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    An unbalanced force must be acting on it.

• No forces at all must be acting on it.

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    All forces on it must be in the same direction.

Answer explanation

For the momentum of the ball to change, an unbalanced force must act on it. This force causes a change in velocity, which directly affects momentum, as momentum is the product of mass and velocity.

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