Question

A car is moving with a velocity of $30\, ms ^{-1}$. On applying the brakes, the velocity decreases to $15\, ms ^{-1}$ in $2 \, s$. The acceleration of the car is

• A. $+7.5 \, ms ^{-2}$
• B. $-7.7 \, ms ^{-2}$
• C. $-7.5 \, ms ^{-2}$
• D. $+15\, ms ^{-2}$

Answer 1

Answer: (C)

Given, $v=15\, ms ^{-1}, v_{0}=30 \,ms ^{-1}$ and $t=2\, s$
Using relation, $v=v_{0}+a t$
Acceleration of the car,
$a =\frac{v-v_{0}}{t}=\frac{(15-30) ms ^{-1}}{2 s } $
$=-\frac{15}{2} ms ^{-2}=-7.5\, ms ^{-2}$