question_answer

A car moving at 40 km/h is to be stopped by applying brakes in the next 4.0 m. If the car weighs 2000 kg, what average force must be applied on it?

Answer:

Given, \[u=40km/h\,\,\,=\frac{100}{9}m/s,\,\,\,V=0,\,\,\,s=4m,\] \[m=2000\,kg,\,\,F=?\] We know, F = ma. How to get a? Using, \[a=\frac{{{V}^{2}}-{{u}^{2}}}{2s}=\frac{{{0}^{2}}-{{\left( \frac{100}{9} \right)}^{2}}}{2\times 4}\] \[=\frac{1250}{81}m/{{s}^{2}}\] \[\therefore F=2000\times \frac{1250}{81}=\frac{250\times {{10}^{4}}}{81}=3.1\times {{10}^{4}}N\]