Applied Physics

A weight lifter lifts the weights havig a mass m, at rest on a stand that is at a height h1, above the floor to a second level at a height h₂ above ground, against gravity.

The dfference between  h1  and  h2  is the net height (h) he lifts the weights against gravity.

To calculate the work done in lifting the weights at height h can be found by adaptong our basic work equation

 

Therefore

Work = Force x distance

         = Force of Gravity x heoght

         = Fg x h

 

 Recall that the force of gravity Fg = m x g

Therefore, the work done in lifting an object against gravity can be calculated using the equation  

W = m x g x h

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Example

What is the work done by an elevator on 5 people (800 Kg) inside the elevator, if they all get off on the 4th. floor (12 m above the ground)?

Solution:

Given:
m = 800 Kg, g = 9.8 N/Kg, h = 12 m

Find:  W

W = m x g x h
    = 800 Kg x 9.8 N/Kg x 12 m
    = 94080 Nm
    = 94 080 J