Question

A motor car of mass 200kg is moving with a certain velocity. It is brought to rest by the application of brakes, within a distance of 20 m when the average resistance being offered to it is 500N. What was the velocity of the motor car.

Answer 1

Given,
$$\begin{gathered} \mathrm{Mass}\mathrm{of}\mathrm{motor}\mathrm{car},\mathrm{m}=200\mathrm{kg} \\ \mathrm{Final}\mathrm{velocity},\mathrm{v}=0 \\ \mathrm{Distance}\mathrm{travelled},\mathrm{s}=20\mathrm{m} \\ \mathrm{Acceleration},\mathrm{a}=\mathrm{F}/\mathrm{m}=-500/200=-2.5\mathrm{m}/{\mathrm{s}}^2 \\ \mathrm{Using}, \\ {\mathrm{v}}^2-{\mathrm{u}}^2=2\mathrm{as} \\ 0-{\mathrm{u}}^2=2\times (-2.5)\times 20=-100 \\ \mathrm{or}\mathrm{initial}\mathrm{velocity},\mathrm{u}=10\mathrm{m}/\mathrm{s} \end{gathered}$$