Question

Certain force acting on a 20 kg mass changes its velocity from 5 m s-l to 2 m s-l. Calculate the work done by the force.

Answer 1

First of all we need to find the acceleration, so that we can find force

$a = \frac{2 - 5}{1} = - 3 \: m {s}^{ - 2}$
Now, Force
$f = ma = - 3 \times 20 = - 60$
Work Done is the displacement by a force. Since, displacement is opposite yo the direction of force, it is negative.

Work Done,

$w = fx = - 60 \times 1 = - 60$
Work Done is -60 Joules

Keep in mind that time and displacement is not given so we assumed them as unit.

Answer 2

Hey There ☺

Given →

Force , F = 20 kg

Intial velocity , u = 5 m/s

final velocity , v = 2 m/s

time = 1 s { since it's not specified but velocity are }

Using the equation of motion =>

v = u +at

$\Rightarrow \bold{ \boxed{ a \: = \frac{v - u}{t} }} \\ \\ \Rightarrow \: a \: = \frac{2 - 5}{1} = - 3$

Now using the 3rd equation of motion =>

(v² -u² /2a )= s

on putting the given Value we get =>

$\Rightarrow \: s = \frac{ {2}^{2} - {5}^{2} }{2 \times - 3} = \frac{4 - 25}{ - 6} \\ \\ \Rightarrow \: s \: = \frac{ - 21}{ - 6} = \frac{7}{2}$

Now

Force = 20 × -3

= -60 N

we know ,

Workdone = Force × Displacement

$\Rightarrow \: w \: = -60 \times \frac{ 7}{2} = -210$

Hence Workdone is equal to -210 Joule

Hope this helps you

@Aish☺