Newton's Laws Test Conceptual

Question 0

What is a box with an arrow to the right doing?

Answer 0

It is accelerating to the right. It could be moving to the right and speeding up, or moving to the left and slowing down.

Question 1

A 10kg suitcase is placed on a scale that is in an elevator. When the scale reads 75 N, what is the elevator doing? Explain.

Answer 1

The elevator is accelerating down. Since the weight of the suitcase must be about - 100N, if the scale reads 75N, the Fn is less than Fg. It is either speeding up going down or slowing down moving up.

Question 2

If a box is in equilibrium, what is its motion?

Answer 2

It is either at rest, or moving at a constant velocity.

Question 3

What is the reaction force to the earth pulling a parachutist down?

Answer 3

The parachutist pulls the earth up.

Question 4

To keep an object sliding along frictionless ice at a constant speed you must apply a constant force.

Answer 4

It doesn’t need ANY force to keep going at a constant speed. If you apply a constant force, it will accelerate, not move at a constant speed.

Question 5

If you travel into space, what changes, your mass or your weight? Why?

Answer 5

Your weight. Your mass doesn’t change, but your weight changes when the force of gravity changes.

Question 6

Weight of force or gravity is measured in…

Answer 6

Newtons

Question 7

If a car is driving north, the net force on the car must be north. True or False?

Answer 7

False. The car might be slowing down, in which case the net force is south.

Question 8

For the same two surfaces, __________ friction is always greater than ________ friction.

Answer 8

Static friction is greater than kinetic.

Question 9

A bowling ball and a tennis ball are floating in space. Which one is harder to accelerate and why?

Answer 9

Th bowling ball, because it has more mass and thus more inertia, even in space.

Question 10

Is the normal force more when you pull a box along the ground at an angle of 17 degrees with the horizontal, or when you pull it straight horizontally? Explain.

Answer 10

Fn is greater when you pull horizontally. When you pull horizontally. Fn=Fg. When you pull up at an angle, the ground doesn’t have to work as hard, so the Fn is less.

Question 11

If a student is pushing a desk to the right, going faster and faster, then what do you know about the force of the student on the desk as compared to the force of the desk on the student?

Answer 11

They are equal and opposite. The force of the ground on the student must be more than the force of the desk back on the student.

Question 12

If you are standing on frictionless ice with a handful of marbles, how do you get off the ice?

Answer 12

You throw the marbles one direction, and you move the opposite direction, but very slowly because your mass is much more than the mass of the marbles.

Question 13

Explain why a book at rest on the seat of your car, stops quickly when you slam on the brakes, in terms of Newton’s first law.

Answer 13

The book was in motion, and wants to stay in motion. When you slam on the brakes, the car stops, but the book continues in motion, so it flies off the seat moving forward.

Question 14

What are all of the forces on a box being pushed with 12 N at a constant velocity across the floor? Is the box in equilibrium? Is there friction? What is it equal to?

Answer 14

Fg, Fn, Ff, and Fp. It is in equilibrium, and friction=-12 N.

Question 15

If a small box slides down a ramp, will there be more friction when the ramp is at a 10 degree angle or a 20 degree angle? Why?

Answer 15

There is more friction when it is sliding down a 10 degree ramp, because Fn is greater.

Question 16

A 1 kg rock and a 20 kg rock are both falling through the air close to the earth. True or False: They have the same force of gravity on them.

Answer 16

False. They have the same acceleration dues to gravity, but not the same Fg.

Question 17

When a piano is sliding down a ramp, what is the net force in the Y direction? What is the normal force equal to?

Answer 17

The net force is zero. The normal force is equal and opposite of Fgy.

Question 18

You push a book across a table at a constant velocity to the right. Which direction is the net force on the book?

Answer 18

The net force is zero (it’s at a constant velocity) and therefore there is no direction.

Question 19

Is there static friction on a box sitting at rest on a table if nothing is touching it but the table? If you push with 51 N, and it still doesn’t move, is there static friction now? How much is it?

Answer 19

No. -51 N. You know because net force =0, so static friction must equal Fp.

Question 20

What two factors affect the force of friction? What factor that we tested in class does NOT affect the force of friction?

Answer 20

Surface type, and normal force (mass or weight) affect friction. Surface area does NOT.

Question 21

If a small car collides head on with a big truck, which object experiences the greatest force? Which object experiences the greatest acceleration? Why?

Answer 21

The forces are equal and opposite. The small car has a greater acceleration because it has a smaller mass, an net force=ma.

Question 22

What is “g” and what is it measured in?

Answer 22

“g” is acceleration due to gravity, and it is measured in m/s/s

Question 23

True or false: A deep space probe is traveling at a constant speed, and suddenly loses its power. It will slow down gradually because of inertia.

Answer 23

False. It will continue at a constant velocity with no forces on it.

Question 24

Which has more mass, 1 kg of iron or 1 kg of feathers?

Answer 24

They have the same mass, since they are both 1 kg.