Name: ____Answer Key_______________
Force and Momentum Calculations
You should remember from your reading last week that Newton’s second law of motion states
that the acceleration of an object is directly proportional to the net force on the object in the same
direction as that net force. This is expressed mathematically as F=ma where F=force, m=mass,
and a=acceleration.
Solve the following problems using this equation (show your work!):
1. You push a friend on a sled. Your friend and the sled together have a mass of 70 kg. If the
net force on the sled is 35 N, what is the sled’s acceleration?
F=ma so a=F/m
a=35 N/70 kg = 0.5 m/s2
2. If the mass of a helicopter is 4500 kg and the net force on it is 18,000 N, what is the
helicopter’s acceleration?
F=ma so a=F/m
a=18,000 N/4,500 kg = 4 m/s2
3. An 85 kg mass has an acceleration of 5.5 m/s2. What is the net force applied?
F=ma
F=85 kg x 5.5 m/s2 = 467.5 N
4. What is the mass of an object that has an acceleration of 55 m/s2 when a net force of 20 N is
applied? (round to the nearest tenth)
F=ma so m=F/a
m=20 N/ 55 m/s2 = 0.3636 kg = 0.4 kg
Another property of motion is called momentum. It is related to how much force is required to
change an object’s motion. It is expressed mathematically as p=mv where p=momentum,
m=mass, and v=velocity.
Solve the following problems using this equation (show your work!):
5. If a 40-kg mass is moving at a speed of 85 m/s, what is its momentum?
p=mv
p= 40 kg x 85 m/s = 3,400 kg∙m/s
6. If a 5000-kg mass is moving at a speed of 43 m/s, what is its momentum?
p=mv
p=5000 kg x 43 m/s = 215,000 kg∙m/s
7. How fast must a 50-kg mass travel to have a momentum of 1500 kg∙m/s?
p=mv so v=p/m
𝑣=
1500 𝑘𝑔 ∙ 𝑚/𝑠
= 30 𝑚/𝑠
50 𝑘𝑔
8. What is the mass of an object that has a momentum of 5000 kg∙m/s when it is travelling at
250 m/s?
p=mv so m=p/v
𝑚=
5000 𝑘𝑔 ∙ 𝑚/𝑠
= 20 𝑘𝑔
250 𝑚/𝑠