Question

A body of mass 20g changes its linear momentum from 8kgm/s to 4kgm/s. Calculate the work done.
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Answer 1

Answer:

W =24 J

Explanation: W = change in KE

Answer 2

Given : A body of mass 20g changes its linear momentum from 8kgm/s to 4kgm/s.  

To Find :   work done.  

Solution:

mass = m = 20 g  = 20/1000  =  0.02  kg

momentum  =  mass * velocity

Initial momentum  =   8kgm/s

=> 0.02 * v₁  = 8

=>  v₁ = 400 m/s

Kinetic energy = (1/2)mv²

Initial  Kinetic energy = (1/2)(0.02)(400)²  = 1600 J

Final momentum  =   4 kgm/s

=> 0.02 * v₁  = 4

=>  v₂= 200 m/s

Final  Kinetic energy = (1/2)(0.02)(200)²  = 400 J

Work Done = Change in Kinetic energy

=  Final  Kinetic energy  - Initial  Kinetic energy

=  400 - 1600

= - 1200 J

= - 1.2 kJ

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