Question

A car moving at a speed v is stopped by a retarding force F in a distance s. If the speed of the car is 3v, the force needed to stop the car in a same distance will be

• A. 3 F
• B. 6 F
• C. 9 F
• D. 12 F

Answer 1

Answer: (C)

9 F

Let the car stops in S distnace

when force =F , then retardation on car a=$\frac{-F}{m}$

the final velocity is 0

using $V^2-U^2=2as$ also $U=v,V=0$

we get $v^2=\frac{2sF}{m}$ ...(1)

now let $F_1$ is applied to stop car in S distance with initial velocity $U=3v$ ,we get

$(3v{)}^2=\frac{2F_{1}s}{m}$ ....(2)

from (1) and (2)

$F_1=9F$