Question

A constant retarding force of 100 N is applied to a body of mass 20 kg moving initiall
25 m/s. How long does the body take to stop?
(A) 9 sec
(B) 4.5 sec
(C) 5 sec
(D) 10 sec​

Answer 1

Solution:

We know that:

$\boxed{\sf{Retardation\:(a) = \frac{F}{m}}}$

So, we get:

$\implies$ 100/20

$\implies$ 5 m/s^2

Since it is retardation, it's acceleration becomes negative.

Therefore: a= -5 m/s^2

Now, using:

$\huge{\boxed{\sf{v = u + at}}}$

We get:

$\implies$ v = u + at

$\implies$ 0 = 25 + (-5)t

$\implies$ t = 25/5

$\implies$ t = 5 seconds

Therefore:

The body takes 5 sec to stop.

Correct option: (C) 5 sec

________________

Answered by: Niki Swar, Goa❤️

Answer 2

Explanation:

Given :

u = 25m/s

F = 100N.

m= 20kg

so, a f/m = 5m/S2

the by the equation v = u +at ,

since v=0

0 = 25 + 5t

t = 5sec.