# A weight lifter lifts 100kg of weight from the floor to a position over her head, 2.2m above the ground. How much work did she do on the mass and how much potential energy (PE) does the mass now...

A weight lifter lifts 100kg of weight from the floor to a position over her head, 2.2m above the ground. How much work did she do on the mass and how much potential energy (PE) does the mass now have with respect to the floor?

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### 1 Answer

The weight lifter lifts 100 kg of weight from the floor to a position over her head, 2.2 m above the ground.

When the mass is lifted to a height of 2.2 m above the ground it acquires a gravitational potential energy equal to m*g*h where m is the mass of the weights, g is the acceleration due to gravity and h is their height with respect to the ground. The potential energy is 100*2.2*9.8 = 2156 J.

The weight lifter has to do this amount of work on the weights for them to reach the height they are at. Or the work done by the weight lifter is 2156 J.

You do not need to use velocity, calculate kinetic energy, etc. in this problem. Kinetic energy is the energy that a body has due to the fact that it is moving. If an external force causes a change in the velocity of the body then the formulas related to kinetic energy need to be used. In this problem, there is only a change in potential energy of the weights due to work being done on them by the weight lifter. The velocity of the weight is not relevant as it is 0 when the weights are on the ground and when they have been raised.