Question

A car is moving with a speed of 40$Km/hr.$ If the car engine generates $7$ kilowatt power, then the resistance in the path of motion of the car will be- -

• A. $360N$
• B. $630N$
• C. zero
• D. $280N$

Answer 1

The correct option is B $630N$

power $=$ Force$\times$ Speed

here in the case$:$ the engine has to deliver power against resistance $($Force$)$ to maintain a constant speed$.$

Resistance$=$ $\frac{power}{speed};$

Given$,$

Power$=7$ $kW=7000W$

Speed $=40km/h$ $=40\times \frac{5}{18}m/s$

$=11.11m/s$

Resistance $=\frac{7000}{11.11}=630.063N$

Hence,

option $\left(B\right)$ is correct answer.