Question

A net force of 100 newtons is applied to a 20 kg cart that is already moving at 3 meters per second. The final speed of the cart was 8 m/s. For how long was the force applied?

Answer 1

F=ma

F=m(∆v/t)

Solving for timt (t):

t=(m∆v)/F

Where

t=?
m=20.0kg
∆v=8m/s-3m/s=5m/s
F=100N

Solve for t:

t=(20kg*5m/s)/100N

t=1s

Answer 2

I assume that the force was applied exactly in the direction of motion

change in momentum = 20(8-3)
= 100 kg m/s

Force = change in momentum /change in time
which is another way of saying F = ma

100 N = 100 kg m/s / change in time

so change in time = 1 second