Question

A 60kg person jumps onto the floor from a height of 3.00m. If he lands stiffly (with his knee joints compressing by 0.500 cm), Calculate the force on the knee joints.

Answer 1

Explanation:

Step 1

Given:

mass of person (m) = 60 kg.

height of jump (h) = 3.0 m.

joints compressed (x) = 0.5 cm. = 0.005 m.

Step 2

Person stated at height contain potential energy. when he jumps, his potential energy converts into kinetic energy and at floor the kinetic energy becomes zero. The work done by floor on knee of person is equal to the kinetic energy.

The work done by floor is,

Physics homework question answer, step 2, image 1

Angle will be 180 in between force and displacement because force exerted on knee is in upward direction and direction of displacement is downward.

Step 3

Change in potential energy will be equal to kinetic energy.

Physics homework question answer, step 3, image 1

this change in potential energy will be equal to work done.

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