P Sci NCFE practice 1

P Sci NCFE practice 1

Multiple Choice

A 100 kg student kicks a 1.5 kg ball with a force of 450 N. What force does the ball apply on the student?

• 4.5 N

• 300 N

• 450 N

• 675 N

Newton's 3rd Law

For every action there is an equal and opposite reaction!

Multiple Choice

A desk exerts an upward force of 1.5 N to a book lying on it. What force does the book exert on the desk?

• a downward force of 0.0 N

• a downward force of 1.5 N

• a downward force of 6.5 N

• a downward force of 15 N

Don't forget about Newton's Laws!

• Newton's 1st law: An object in motion stays in motion, an object at rest stays at rest unless acted upon by an outside force.

• Newton's 2nd law: F = ma

• Newton's 3rd Law: For every action there is an equal and opposite reaction.

Multiple Choice

A large rock has a mass of 750 kg. What is its weight?

• 76.5 N

• 7350 N

• 759.8 N

• 740.2 N

Gravity

Remember, weight is the pull of gravity on an object's mass. Gravity on Earth is 9.8 so to find weight we use the equation Fg (weight) = m g

Multiple Choice

A student applies a force to a box with a mass of 30 kg. If the student applies the same force to a box with a mass of 15 kg, which best describes the effect on the acceleration of the 15 kg box?

• It is half the acceleration of the 30-kg box.

• It is double the acceleration of the 30-kg box.

• It is the same as the acceleration of the 30-kg box.

• It is triple the acceleration of the 30-kg box.

Force = mass x acceleration

• So, if the force is constant but the mass is cut in half, the acceleration will be doubled!

• Ex) 60 N = 30 kg x a, a = 2 m/s2

• 60 N = 15 kg x a, a = 4 m/s2

Multiple Choice

Two students pull on the opposite ends of a rope, but neither student is able to move the other. Which statement best explains why neither student is moved?

• They each pull on the rope with the same amount of force, so the net force is zero.

• They each exert the same amount of friction against the ground, so the net friction is zero

• Their forces are not balanced, but gravity keeps them from moving.

• The two students have the same mass.

Newton's Laws again!

Remember, if the forces are equal, the object will not move! So if both sides are exerting the same force, the net force is 0 and they won't move!