Question

A runner of mass 59.5 kg initially moves at a speed of 9.50 m/s. How long must an average external force of 1.90 102 N act to bring the runner to rest

Answer 1

Hi there!

We can use the Impulse-Momentum Theorem to solve.

Recall:

Impulse = Change in momentum = Δp = mΔv

The change in momentum is equivalent to:

Δp = m(vf - vi) = (59.5)(0 - 9.5) = -565.25 kgm/s ⇒ 565.25 kgm/s (+ b/c change)

This is also equal to the impulse, which is:

I = Ft (Force × time)

Thus:

565.25 = (1.9 × 10²)t

565.25/190 = 2.975 sec