A car moving at 10.0 m/s crashes into a barrier and stops in 0.050 s. There is a 20.0-kg child in the car. Assume that the child's velocity is changed by the same amount as that of the car, and in the same time period. What is the impulse needed to stop the child?

The impulse needed to stop the child = - 200 Ns

Explanation:

Impulse: This can be defined as the product of force and time of a body. The S. I unit of impulse is kgm/s or Ns

From newton's second law,

I = mΔv ... Equation 1.

Where I = Impulse needed to stop the child, m = mass of the child, Δ = change in velocity of the child.

Given: m = 20.0 kg,

Δv = v-u where v = 0 m/s, u = 10.0 m/s

Δv = 0-10 = - 10 m/s.

Substituting into equation 1

I = 20 (-10)

I = - 200 Ns.

Thus the impulse needed to stop the child = - 200 Ns

Note: The negative sign shows that the impulse act against the motion of the child