A ball is lying on a table. The forces on the ball are sketched on the right. N mg

Here N is the force of the table pushing up on the ball, to keep it from going through the table.

Newton’s third law says that for every force there is an equal and opposite force. What is the 3rd-law force pair for the weight of the ball

(a) mg

(b) N

(c) the upwards force of gravity on the Earth due to the ball

(d) None of the above

In the sketch on the right, a book lies on the table.

Which are the correct 3rd-law force pairs?

(a) The force of the Earth’s gravity on the book and the normal force of the table on the book.(b) The force of Earth’s gravity on the book and the gravitational attraction of the book on the Earth.

(c) The weight of the book and the force from the table that keeps the book from falling through the table.

(d) None of the above.

W=mg

Nfk =µkN

T

A block is being pulled up a ramp, with the free-body diagram shown on the right.

What is the third-law force corresponding to the weight mg of the block?

(a) N sin

(b) N cos

(c) fk

(d) N cos - fk sin +T sin

(e) None of the above

a

A car accelerates without its wheels slipping on the pavement. There is a static friction force between the wheels and the pavement of fs. Which figure below best represents the free body diagram of a wheel? Assume the weight of the wheel is negligible compared to the weight of the rest of the car.

Nroad

fs

a)

Fcar on axle

Nroad

fs

b)

Fcar on axle

Nroad

fs

c) Fcar

Fcar on axle

Which of the following vector pairs best represents the forces on two balls of different size in outer space?

a)

e)

b)

c) d)

A locomotive pulls a series of wagons. Which is the correct analysis of the situation?

a) The locomotive moves forward because the locomotive pulls forward slightly harder on the wagons than the wagons pull backward on the locomotive.

b) Because action always equals reaction, the locomotive cannot pull the wagon the wagons pull backward just as hard as the locomotive pulls forward, so there is no motion.

c) The locomotive’s force on the wagons is as strong as the force of the wagons on the locomotive, but the frictional force on the locomotive is forward and large while the backward frictional force on the wagons is small.

d) The locomotive can pull the wagons forward only if it weighs more than the wagons. PI