Find the force required to stop a car of mass 100Kg with two passengers of
50 g each sitting inside,if it is moving at 60km/h speed and takes 5s to stop.

It is given that:

• Mass of car = 100 kg
• Two passengers with each of a mass of 50 g = 0.05 kg
• Initial velocity = 60 km/h = 60 (5/18) = 50/3 m/s
• Car takes 5 s to stop

Initial velocity u = 50/3 m/s
Final velocity  v = 0
$$\begin{gathered} v = u +at \\ a =\frac{v-u}{t} =\frac{0-50/3}{5} =-\frac{10}{3} m/s^2 \\ Negative sign shows that this is deceleration. \\ Total mass = mass of car+ mass of 2 passenger = 100 +2(0.050) =100 +0.1=100.1 Kg \\ Force = ma \\ Here a represents deceleration \\ F =100.1\times \frac{10}{3} =\frac{1001}{3} =333.67N \end{gathered}$$

Regards