Calculate the final velocity right after a 112 kg rugby player who is initially running at 7.95 m/s collides

Question

Calculate the final velocity right after a 112 kg rugby player who is initially running at 7.95 m/s collides head‑on with a padded goalpost and experiences a backward force of 17700 N for 5.50×10−2 s.

What is the final velocity?

Answer 1

The player's momentum change equals the impulse of the force, 17700x5.5e-2, which reduces his momentum, and therefore the final velocity is

(112*7.95 - 17700*5.5e-2)/112 = -0.742

Answer 2

F Δt=mΔv .... 17700*.055=112*(v-7.95) solve to find v= 8.04 m/s