# Physics

posted by Sarah

A 55 kg pole vaulter falls from rest from a height of 5m onto a foam rubber pad. The pole vaulter comes to rest .3s after landing on the pad.
A) calculate the athlete's velocity just before reaching the pad
B) calculate the constant force exerted on the pole vaulter due to the collision

1. Damon

same as the last problem but you need initial velocity to get initial momentum
v = Vi - g t
v = 0 - g t so t = v/g

h = Hi + Vi t - (1/2) g t^2
0 = 5 + 0 t - (g/2) t^2
0 = 5 - (g/2)(v^2/g^2)
10 = v^2/g
v^2 = 10 g = 98

or use energy
(1/2) m v^2 = m g h
v^2 = 2 g h = 10 g = 98

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