Question

Calculate the amount of work required to stop a car of 1800kg moving with a velocity of 30 km/h

Answer 1

The required work is "7.497 kJ".

Explanation:

Given,

Mass of the car(m) = 1800 kg and

Veocity = 30$\dfrac{km}{m}$

= $30\times\ \dfrac{5}{18}\dfrac{km}{hr}$

= 8.33 $\dfrac{m}{s}$

∴ Work done = Change in kinetic energy

Work done = Final kinetic energy  Initial kinetic energy

∴ Required work done = $\dfrac{1}{2}$·m·$v^{2}$  $\dfrac{1}{2}$·m·$u^{2}$

Where, final velocity, v = 0 and initial velocity, u = 8.33$\dfrac{m}{s}$

∴ Work done = Final kinetic energy  Initial kinetic energy

= $\dfrac{1}{2}$·1800·$0^{2}$  $\dfrac{1}{2}$·1800·$(8.33)^{2}$

= 0 - 7497 J

= 7.497 kJ

Hence, the required work is "7.497 kJ".