# A person doing a chin-up weighs 653N, exclusive of the arms. A person doing a chin-up weighs 653N, exclusive of the arms. During the first 21.8cm of the lift, each arm exerts an upward force of...

A person doing a chin-up weighs 653N, exclusive of the arms.

A person doing a chin-up weighs 653N, exclusive of the arms. During the first 21.8cm of the lift, each arm exerts an upward force of 374N on the torso. The acceleration of gravity is 9.8m/s^2.

**If the upward movement starts from rest, what is the person's velocity at this point? Answer in units of m/s**

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### 1 Answer

The person doing he chin-up weighs 653 N exclusive of the arms. During the first 21.8 cm of the lift a force of 374 N is exerted by each arm on the torso. The total force exerted by the person's two arms on the torso is 374*2 = 748 N.

As the weight of the person is 653 N, the net force on the torso is 748-653 = 95 N.

The acceleration due to gravity is 9.8 m/s^2. This gives the mass of the person as 653/9.8= 66.63 kg. The acceleration of the person as the chin-up is done is 95/66.63 = 1.425 m/s^2.

The upward movement starts from rest, use the formula v^2 - u^2 = 2*a*s

=> v^2 - 0 = 2*1.425*21.8*10^-2

=> v^2 = 31.1

=> v = sqrt 31.1 = 5.57 m/s

The velocity of the person after the first movement of 21.8 cm during the chin-up has been completed is 5.57 m/s