Asked by Paul

Severe stresses can be produced in the joints by jogging on hard surfaces or with insufficiently padded shoes.If the downward velocity of the leg is 7.3m/s when the joggers foot hits the ground. If the leg stops in a distance of 1.1 cm. Calculate the force on the ankle joint. The mass of the joggers leg is 9.5 kg

Answers

Answered by Damon
stops in .011 meter
average speed during deacceleration = 7.3/2 = 3.65 m/s
so time to stop = .011/3.65 = .00301 second

momentum change = 9.5 * 7.3 = 69.4 kg m/s

so F = d (mv)/dt = 69.4 kg m/s / .00301 s

= 23012 kg m/s^2 or Newtons

Note - I used Newtons original second law which is Force = rate of change of momentum. For constant mass this is F = m a
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