Question

# 17. Action-reaction forces in third Newton’s law: a. Always act on the same object. b. Sometimes...

17. Action-reaction forces in third Newton’s law:

a. Always act on the same object.

b. Sometimes act of the same object.

c. Always act on different objects.

d. May or may not be antiparallel to each other.

18. If force exerted by horse on a cart is equal and opposite to the force exerted by cart on a horse, how does horse manage to move a cart?

a. Horse has bigger mass than a cart.

b. Horse still exerts greater force on a cart, than cart exerts on a horse.

c. Horse has an acceleration helping it to move a cart.

d. Horse usually goes down along inclined plane.

e. Horse moves cart using force of friction between ground and hooves.

f. Horse moves cart using its weight.

1.1 What kind of friction is experienced by the tires of your car?

a. Kinetic

b. Static

c. Both kinetic and static

d. There is no friction between tires and road.

1.2 If your car moves to the north along straight line, what is direction of force of friction experienced by tires?

a. South

b. North

c. East.

d. West.

e. Impossible to determine.

20. You are sitting inside of a crate standing on a very smooth ice on the surface of some lake.

You decided to move this crate towards the shore: still sitting inside you start to push crate from inside against one of its walls. Will this crate move? Why and why not?

1. This crate will move because you are applying some unbalanced force.
2. This crate will move because force which you exert on a crate is greater than force exerted on you by a crate.
3. This crate will not move because action-reaction force (you on crate and crate on you) are internal forces of a system.
4. This crate will not move because action-reaction forces (you on crate and crate on you) are external forces of a system.
5. This crate will move because there is no friction.

21. Check how you understand Newton’s laws.

1.1 An object is sitting at rest on a horizontal table. Which one of three Newton’s laws predicts that normal force acting on this object is equal in magnitude and opposite in direction to the force of gravity (weight) acting on this object?

a. First

b. Second

c. Third

d. Law of gravitation.

1.2 If force of gravity acting on this object is “action force”, what will be “reaction force”?

a. Normal force acting on an object.

b. Normal force acting on a table.

c. Force of gravity exerted by an object on Earth.

d. Force of gravity exerted by Earth on object.

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