An object of mass 4kg falls from height 44.1m and reaches the ground with speed 24.5 m/s. Find the work done by air friction on the object.

Solution

Given,
Mass of the object, m = 4 kg
Height from which the object falls, h = 44.1 m
Speed with the mass is falling, v = 24.5 m/s
The work done by gravity on the object,
$straight W subscript 1 equals mgh equals 4 cross times 9.8 cross times 44.1$
$space space space equals 1728.72 straight J$

Increase in kinetic energy of object is,
$increment straight K equals 1 half mv squared space space space space space space equals 1 half cross times 4 cross times left parenthesis 24.5 right parenthesis squared$
= 1200.5J
Therefore work done by friction is,
$straight W subscript straight f equals straight W subscript 1 minus increment straight K$
$equals 1728.72 minus 1200.5$
$equals 528.22 space straight J$