A 60 kg dancer leaps 0.32m high.
With what momentum does the dancer reach the ground?
What impulse is needed to make a stop?
As the dancer lands, the knees bend, lengthing the stopping time to 0.050 seconds. FInd the average force exerted on the body.
Compare the stopping force to the performer's weight.

I need help on this question
Any help and explanation is appreciated

Question

A 60 kg dancer leaps 0.32m high. 
With what momentum does the dancer reach the ground?
What impulse is needed to make a stop?
As the dancer lands, the knees bend, lengthing the stopping time to 0.050 seconds. FInd  the average force exerted on the body. 
Compare the stopping force to the performer's weight.


I need help on this question
Any help and explanation is appreciated

festinger · Answer

When the dancer comes down from a height of 0.32m, the dancer gains that amount of kinetic energy. Using mgh=0.5mv^2, you can find the speed v when the dancer reaches the floor.

Taking the definition of momentum, p=mv, you should find that 150 (units)

When the dancer stops, v is 0, this p=mv is 0. Impulse is the change of momentum, which is difference in momentum when the dancer stops and the momentum when the danccer just reaches the floor. Which makes it -150 (units)

Force is the rate of change of momentum, and thus it is the change in momentum divided by the time needed to create that change, and thus it is -150/0.05 = -3000N. That's about 5 times the dancer's weight!