Question

A given $1700kg$ car goes from $18m/s$ to $0m/s$. If this transition took $9sec$, what was the average power supplied by the force causing this deceleration?
Take the car system to be otherwise isolated (i.e. the decelerating force was the only force acting on the car).

• A. $-1700W$
• B. $-15300W$
• C. $-30600W$
• D. $-61200W$
• E. Cannot be determined from the information given

Answer 1

The correct option is C $-30600W$

Given : $u=18$ m/s $u=0$ m/s $m=1700$ kg $t=9$ s

Using $v=u+at$

$\therefore$ $0=18+a\times 9$ $⟹a=-2$ $m/s^2$

Using $v^2-u^2=2aS$

$\therefore$ $0-(18{)}^2=2(-2)S$ $⟹S=81$ m

Thus work done by decelerating force $W=-maS$

$\therefore$ Power supplied $P=\frac{-maS}{t}=\frac{-1700\times 2\times 81}{9}=-30600$ W