Question

A motorist drives north for 30mins at 85km/h and then stops for 15 mins.He continous traveling north and covers 130 km in 2 hours. what is his total displacement and average velocity?

Answer 1

Dear student,
Let us consider the north to be positive direction of motion,

First the motorists travels with velocity v , for 30 min.

So first displacement is given by $∆x_1=v(∆t)$
=85km/hr(35min/60min)

$∆x_1$ =49.58km

Displacement when motorists is at rest $∆x_2=0$
displacement while travelling next 2hrs is $∆x_3=130km$

thus the total displacement $∆x_{tot}=∆x_1+∆x_2+∆x_3$
$∆x_{tot}=$49.58+0+130
$∆x_{tot}=179.59$ km.

The total time taken is $∆t_{tot}=∆t_1+∆t_2+∆t_3$
=(35+15)/60 +2 hour = 2.83 hr

The average velocity is given V_{av = $\raisebox{1ex}{$∆x$}\!\left/ \!\raisebox{-1ex}{$∆t$}\right.$}
=179.39/2.83
V_av=63.45 km/hr.

_Regards.