8th Grade Unit 1 Review

A baseball bat hits a baseball with a force of 100 Newtons. What is the force and its direction exerted by the ball on the bat?

• 100 Newtons, same direction

• 100 Newtons, opposite direction

• 200 Newtons, same direction

• 200 Newtons, opposite direction

According to Newton's Third Law, if someone jumps off a skateboard, the skateboard will roll backwards because -

• the mass of the skateboard is the same as the mass of the person jumping off

• the pull of gravity on the person is the same as on the skateboard, regardless of size.

• the air resistance on the person is great and the friction on the skateboard is small.

• for the force that sent the person forward, there is an equal force pushing back on the skateboard.

The nozzle of a rocket is pointed downward so that as fuel is ignited, the exhaust pushes downward. Why is this arrangement necessary for a rocket to function properly?

• The rocket is protected from the heat of the exhaust.

• Burned fuel can be collected on the ground.

• As fuel is combusted, the rocket pushes the gases backward and the gases push the rocket forward.

• This allows the rocket to be steered properly.

Newton's third law describes action and reaction forces. A table of four scenarios is provided.

Which of the scenarios described in the table show equal and opposite reaction forces?

• The rocket and balloon

• The rocket and train

• The balloon and girl

• The train and girl

The head of a hammer must be strong to resist what force?

• The force of the air resistance on the moving hammer

• The force of the person using the hammer

• The force of gravity pulling down on the hammer

• The force of the nail pushing in the opposite direction

The illustration shows the forces in Newtons (N) acting on three different blocks.

Which boxes will move under these conditions?

• Blocks 1 and 2

• Blocks 2 and 3

• Blocks 1 and 3

• Blocks 1, 2, and 3

The illustration shows all the forces in Newtons (N) acting on a box. The sum of all the forces acting on the box results in a force acting on the box-

• to the right with a strength of 11 Newtons.

• to the left with a strength of 7 Newtons.

• to the right with a strength of 25 Newtons.

• to the left with a strength of 6 Newtons.

Students are investigating how mass affects the force needed to move an object. They attached a wooden block to a spring scale and placed a 10 g mass on top of the block and pulled it 50 cm across the table.

Which of the following changes to their setup would result in a larger force reading on the spring scale?

• Sliding the block 60 cm

• Attaching a larger spring scale

• Using a 20 g mass

• Using a circular piece of wood

Students are using an air rocket to investigate the relationship between force and an object's motion.

Students pump air into the rocket, then release the rocket, and the compressed air pushes the rocket upward.

In order to vary the amount of force acting on the rocket, which of the following should the students change in each trial?

• The length of the hose attached to the pump

• The distance traveled by the rocket

• The amount of air pumped into the rocket

• The height of the rocket from fins to cone

Which of the following graphs shows how the mass of an object affects the amount of force needed to move it?

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