1. Chapter 3
Newton’s Laws
Practice Exercise
Solutions

2. 1. Of the following, the one most closely related to inertia is:
A) weight
B) acceleration
C) mass
D) force
2. If your mass is 75kg, the magnitude of the Earth’s gravitational pull on you is:
A) 132N
B) 588N
C) 600N
D) 735N

3. A) zero
B) 2N
C) 10N
D) 50N
4. If you observe an object which is not moving you can conclude that no forces are acting on it.
You can only conclude that no NET FORCE is acting on it, there may be any number of forces acting on the object…we can only conclude that the sum of the forces is zero.
A) True
B) False

4. 5. Constant acceleration is to net force as constant velocity is to:
A) weight
B) inertia
C) free-fall
D) work
Motion at a constant acceleration is caused by a net force.
Motion at a constant velocity is caused by inertia.
6. Action and reaction forces never cancel each other because:
A) they are not equal
B) they act on different objects
C) they are not opposite to each other
D) all of these reasons

5. 7. If the net force acting on an object is doubled and the mass of the object is kept constant, the acceleration of the object will be multiplied by:
The acceleration of an object is directly proportional to the net force acting on it. If the net force is multiplied by some factor and the mass is held constant the acceleration will be multiplied by the same factor. Doubling the net force will double the acceleration.
A) 1/2
B) 2
C) 1/4
D) 4
The acceleration is inversely proportional to the object’s mass. Multiplying the mass by some factor and keeping the net force constant will multiply the acceleration by the reciprocal of that factor. Doubling the mass will multiply the acceleration by 1/2.

6. 8. A 15kg object is initially moving at 100m/s to the right
8. A 15kg object is initially moving at 100m/s to the right. The net force required to stop the object in 5s is:
A) 60N
B) -60N
C) 300N
D) -300N
Accelerated Motion

7. 9. A 20kg box is being pulled to the right along a level floor by a force of 90N. If the acceleration of the box is 2.5m/s2, the force of kinetic friction between the box and the floor must be:
A) -20N
B) -30N
C) -40N
D) -50N

8. 10. The upward force required to lift an 11kg object at a constant velocity is:
B) 215.6N
C) 312.4N
D) zero

9. 11. A 7.5kg object is acted upon by two horizontal forces: F1 is 35N to the left, F2 is 80N to the right. The acceleration of the object is:

10. 12. A person standing at the bottom of a 30m high tower throws a 2kg ball straight up with an initial velocity of 25m/s. Will the ball reach the top of the tower?
A) Yes
B) No
Free-Fall

11. 13. A. 2kg helium balloon is acted upon by a buoyant force of 4N
13. A .2kg helium balloon is acted upon by a buoyant force of 4N. If released from rest the time required for the balloon to reach an altitude of 200m would be:
A) 6.3s
B) 14.1s
C) 18.5s
D) 22.6s
Accelerated Motion

13. 14. Ball A is dropped from a cliff 100m high
14. Ball A is dropped from a cliff 100m high. At the same time Ball B is thrown horizontally from another cliff 100m high. The paths followed by the two balls are shown below.
The ball that reaches the ground first will be:
A) Ball A
B) Ball B
C) they will reach the ground at the same time
D) the initial velocity of Ball B must be known