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# Tag Archives: Work done

## Work done – Man jumps from height 3 m, what is the force exerted by his legs?

A boy of mass 40 kg jumps from rest from a platform of height 3 m. He lands by bending his knees and stops his body in 0.5 s after landing. What is the force exerted by his legs?

**Solutions: 620 N**

To solve this question, you need to apply conservation of energy (COE) to find the kinetic energy (KE) that the boy possesses just before he reaches the ground.

After which, you can solve the question using (1) Conservation of energy or (2) Kinematics to solve.

Using COE to find the KE just before he reaches the ground.

**Method 1: Using Conservation of Energy (COE)**

**Method 2: Using Kinematics**

You must know these 2 methods and always think along this 2 directions when dealing with such questions.