Calculate the final speed of a 100-kg rugby player who is initially running at 7.00 m/s but collides head-on with a padded goalpost and experiences a backward force of 15 kN for 50 ms.

Given Information:

Mass = m = 100 kg

Time = Δt = 50 ms

Initial speed = Vi = 7.00 m/s

Force = F = 15 kN

Required Information:

Final speed = Vf = ?

Answer:

Vf = - 0.5 m/s

Explanation:

As we know the Impulse is given as

I = - FΔt

Where negative sign indicates backward force

I = - 15,000*0.050

I = - 750

From the impulse-momentum relation, we can write

I = mVf - mVi

Where Vf is the final speed of the rugby player and Vi is his initial speed

mVf = I + mVi

Vf = (I + mVi) / m

Vf = (-750 + 100*7) / 100

Vf = - 0.5 m/s

Therefore, the final speed of the rugby player is - 0.5 m/s