Name: _______________________________
Newton’s First, Second and Third Laws Practice
1. True or False?
•
An object moving with constant velocity has no forces on it. _____
•
An object moving in a circle must have a force acting on it.
_____
•
An object can have a changing velocity when FNet = 0.
_____
•
When a = 0 for an object, FNet must equal zero.
_____
•
When a = 0, an object’s velocity must equal zero.
_____
•
When an object’s speed is constant, it implies a = 0.
_____
•
FNet = 0 implies a = 0 and a = 0 implies FNet = 0.
_____
•
FNet = 0 and a = 0 both imply a constant velocity.
_____
•
A constant velocity implies both FNet = 0 and a = 0.
_____
2. Calculate the acceleration of the blocks and the tension in each cord assuming there is
no friction.
5.0 kg
FT1
2.0 kg
FT2
5.0 kg
24 N
3. Calculate the acceleration of the blocks and the tension in each cord assuming the
coefficient of friction between the blocks and the surface is 0.10.
5.0 kg
FT1
2.0 kg
FT2
5.0 kg
24 N
4. Find the tensions in the strings.
40o
60o
T2
T1
10 kg
5. While two forces act on it, a particle moves at the constant velocity 3 î  4 ĵ
m
. One
s
of the forces is 2 î  6 ĵ N . What is the other force?
6. Three astronauts, propelled by jet backpacks, push and guide a 120 kg asteroid toward
a processing dock. They exert forces of F1 = 32 N at 30o, F2 = 55 N at 0.0o and F3 = 41 N
at 60°. Find the asteroid's acceleration:
A. In unit-vector notation
B. As a magnitude and direction relative to the positive x axis
7. A 0.150 kg particle moves along an x axis according to x(t) = -13.00 + 2.00t + 4.00t2 3.00t3, with x in meters and t in seconds. In unit-vector notation, what is the net
force acting on the particle at t = 3.40 s?
8. Four disks are suspended by cords as shown. The top cord loops
over a frictionless pulley and pulls with a force of magnitude 98 N
on the wall to which it is attached. The tensions in the three
shorter cords are T1 = 58.8 N, T2 = 49.0 N, and T3 = 9.8 N. What
are the masses of the four disks?
Solutions:
1. F T F T F F T T T
m
2. a = 2.0 2
FT1 = 10 N
s
m
3. a = 1.0 2
FT1 = 10 N
s
4. T1 = 51 N
FT2 = 14 N
FT2 = 14 N
T2 = 78 N

5. F2   2 î  6 ĵ N

m
6. A. a  0.86 î  0.43 ĵ 2
s
m
B. a  0.96 2
  27 o
s

7. F   7.98 î N
8. mD = 1.0 kg
mC = 4.0 kg
mB = 1.0 kg
mA = 4.0 kg