Question

A 65-kg person jumps from the first floor window of a burning building and lands almost vertically on the ground with a horizontal velocity of 3 m/s and vertical velocity of −9m/s. Upon impact with the ground he is brought to rest in a short time. What is the force on the feet of the person jumping from the burning building, considering stiff knees and bent knees?

a) Stiff knees: 637 N, Bent knees: 480 N
b) Stiff knees: 480 N, Bent knees: 637 N
c) Stiff knees: 637 N, Bent knees: 320 N
d) Stiff knees: 320 N, Bent knees: 637 N

Answer 1

The force experienced by the feet when a person jumps and lands depends on whether they keep their knees stiff or bend them. With stiff knees, the force is 637 N, while with bent knees, the force is 320 N.

Step-by-step explanation:

When a person jumps from a height and lands, the force experienced by their feet depends on whether they keep their knees stiff or bend them.

If the person keeps their knees stiff, the force on their feet can be calculated using the equation F = Δp / Δt, where Δp is the change in momentum and Δt is the time taken to come to a stop.

If the person bends their knees, the force on their feet will be smaller because the bending of the knees helps to extend the stopping distance, reducing the force exerted on the feet.

The force on the feet with stiff knees is 637 N, while the force on the feet with bent knees is 320 N.