. The velocity of a body with a mass of 100 kg increases from 4 m/s to 8 m/s when
a force acts on it for 2 s. Answer the following questions:
(5 marks)
a) Calculate the momentum before the force acts on the body.
b) What is the momentum after the force acts on the body?
c) What is the gain in momentum per second?
d) Calculate the value of the force.
Answers
Answer:
Mass of the body =10 kg
Initial velocity u=4 m/s
Final velocity v=8 m/s
Time t=2s
a) Momentum before force acts p
1
=m×u=10×4=40kg.m/s
b) Momentum after force acts p
2
=m×v=10×8=80kg.m/s
c) Gain in momentum per second =
2
40
=20kg.m/s
d) Acceleration a=
t
v−u
=
2
8−4
=2m/s
2
Force =m×a=10×2 =20N
Answer:
a] the momentum before the force acts on the body = mu
= 100 kg × 4 m/s
= 400 kg.m/s
b] the momentum after the force acts on the body = mv
= 100 kg × 8 m/s
= 800 kg.m/s
c] What is the gain in momentum per second = 400 kg.m/s / 2
= 200 kg.m/s
d] F = ma
= m[v-u]/t
= 100 kg [ 8 m/s - 4 m/s] / 2s
= 100 kg × 4 m/s /2s
= 200 N