Question

A constant retarding force of 100 N is applied to a body of mass 20 kg moving initially with speed 25 m/s. How long does the body take to stop?​

Answer 1

Answer:-

it takes 5 second for body to stop.

Explanation:-

Given:-

Final velocity (v) =0

Initial velocity (u)= 25 m/s

Force( F)= 100 N

Mass of body (m)= 20kg

Solution:-

$\bf{retardation \:(a) = \frac{F}{m} } \\ \\ \implies \: \frac{100}{20} = 5 \: \: \: \frac{m}{ {s}^{2} } \\ \\ \red{ \bf{now \: using \: first \: equation \: of \: motion}} \\ \\ \implies \bf{ v = u + at} \\ \\ \implies \: \bf{ 0 = 25 + ( - 5)t }\\ \\ \implies \: \bf{5t = 25 }\\ \\ \implies \: \bf{t = 5 \: s}$

Hence, it takes 5 second for body to stop.

Answer 2

Answer: The answer is 5 seconds

Explanation:

F = -100N (it is retarded force)

M = 20 kg (given)

U = 25 ms^-1

V= 0 ms^-1

Since,

F = Ma

Therefore, a = F/M

a= -100/20 = -5ms^-2

By using 1st eq.,

V = u + at

0 = 25 + (-5t)

-25 = -5t

t = 5 seconds.

Therefore, the answer is 5 seconds