Unit Test: Energy, Forces, and Collisions

Nathan and Melanie are riding a roller coaster. What happens to the energy of the roller coaster as it moves from the top of a hill (point A) to the bottom (point B)?

• A. Potential energy is transformed to kinetic energy.

• B. Kinetic energy is transformed to potential energy.

• C. Both potential energy and kinetic energy stay the same.

• D. Potential energy decreases and kinetic energy stays the same.

Carlos and Wesley are playing tug-of-war. What is the definition of a force in this context?

• A. A pull exerted on an object

• B. A measure of how heavy an object is

• C. A push or a pull exerted on an object

• D. A change in the direction of motion of an object

When Wesley and Diego studied geological columns from different parts of the world, they discovered something interesting: the fossils of dinosaurs and many groups of reptiles and marine invertebrates disappeared at the top of the Mesozoic section. What is the most likely explanation of this evidence?

• A. The organisms evolved very quickly into new organisms.

• B. Organisms likely migrated to different parts of the world.

• C. An extinction event caused many of the organisms to die off.

• D. The areas no longer had the conditions needed for fossilization.

Melanie needs to set up a demonstration to prove that Newton’s third law applies during the collision of two objects. She has a toy car, a toy truck, and two identical billiard balls. She chooses to demonstrate the action-reaction force pairs by rolling the billiard balls toward each other. Why did Melanie choose billiard balls instead of the other objects to illustrate her point?

• The billiard balls have the same mass, making the result of equal forces easier to see.

• The toy truck would exert more force on the toy car, showing unequal forces instead of equal ones.

• The billiard balls are the same diameter, showing equal forces during a collision and proving Newton’s third law.

• A collision between any of the other objects would not demonstrate Newton’s third law, making the demonstration invalid.

Wesley and Melanie are testing identical miniature rockets using the same platform. The data collected from one launch are shown in the graph. Which of these describes the relationship between the rocket’s speed and its kinetic energy?

• A. There is no relationship between speed and kinetic energy.

• B. There is a linear relationship between speed and kinetic energy.

• C. There is a constant relationship between speed and kinetic energy.

• D. There is a nonlinear relationship between speed and kinetic energy.

Write an X in the correct box for each statement to show whether each force is a contact force or a noncontact force.

• contact force

• magnetic force

• contact force

• pushing with your hands

• contact force

• air resistance

• noncontact force

• gravity

• noncontact force

• friction

Safwana leaves several tools on the floor of her workshop when she goes for her lunch break. Sometime later Safwana returns and sees that one of her coworkers has moved her tools to different shelves on a nearby bookshelf. Which data would Safwana need to collect to calculate the amount of work required to lift her tools onto the shelves? Circle the letters of all the correct answers.

• the height of each shelf

• the time it took to move each tool

• the amount of force needed to lift each tool

• the strength of the person who moved the tools

Identify the forces acting on the puck at the start of a hockey game when the referee drops the puck between Wesley and Carlos from opposing teams, and the puck does not move even though both players are pushing on it with their hockey sticks.

• Gravitational force and normal force

• Gravitational force, normal force, and frictional force

• Gravitational force, normal force, frictional force, and applied forces from the players

• Only the applied forces from the players

At the start of a hockey game, the referee drops the puck between Carlos and Nathan from opposing teams. Each player wants to push the puck in the opposite direction. For several seconds the puck does not move even though both players are pushing on it with their hockey sticks. Why does the puck not move?

• The puck is too heavy.

• The forces applied by both players are equal and opposite.

• The ice is too slippery.

• The puck is stuck to the ice.

At the start of a hockey game, the referee drops the puck between Genesis and Nathan from opposing teams. Each player wants to push the puck in the opposite direction. For several seconds the puck does not move even though both players are pushing on it with their hockey sticks. How can one of the players get the puck to move?

• By applying more force than the opposing player

• By waiting for the other player to stop pushing

• By using a different stick

• By calling a timeout