Question

A force acting on a 20 kg mass changes its velocity from 5m/s to 2 m/s. Calculate the work done.

Answer 1

According to work k.energy theorem

Work done by force equals change in k.e

So

W=0.5*20(4–25)

W=-210joule

Answer 2

A nswer

Work dine is -210 J

Explanation

Given

A force is acting on a body of mass 20 kg

It changes its velocity form 5 m/s to 2 m/s

To Find

The work Done?

Form ula

Kinetic Energy = ½mv² or ½mu²

Solution

So here we know that the change in the kinetic energy of the body will be the work done

Wo rk Done

➝ Work = ½mv² - ½mu²

v = 2 m/s

u = 5 m/s

Initial Kinetic Energy

➝ ½mu²

➝ ½ × 20 × 5²

➝ ½×20×25

➝ 10×25

➝ 250 J

Final Kinetic Energy

➝ ½mv²

➝ ½×20×2²

➝ ½×20×4

➝ 10×4

➝ 40 J

Work Done by the body

➝ Initial-Final

➝ 40-250

➝ Work = -210 J

Here it is negative as it reduces the speed of the body