Question

You drive a car at a speed of 70 km/hr on a straight road for 8.4 km, and then the car runs out of petrol. You walk for 30 minutes to reach a petrol pump at a distance of 2 km. The average velocity from the beginning of your drive till you reach the petrol pump is?

• A. (a) $16.8km/hr$
• B. (b) $35km/hr$
• C. (c)$64km/hr$
• D. (d) $18.6km/hr$

Answer 1

The correct option is A

(a) $16.8km/hr$

Step 1: Given parameters.

Speed of car ($v_c$) =$70km/hr$

Distance traveled by car($d_c$) =$8.4km$

Walked distance($d_w$) =$2km$

Time taken to complete walk($T_w$) =$30min=0.5hr$

Step 2: Solution.

1. Time is taken by car ($T_c$) =$\frac{8.74}{70}=0.125hr$
2. Total displacement ($d_{total}$)= $8.4+2=10.4km$
3. Total time taken ($T_{total}$) = $0.125+0.5=0.625hr$
4. The average velocity ($v_{av}$) = $\frac{Displacement}{Totaltimetaken}=\frac{10.4}{0.625}=16.64km/hr$

An answer is an option (A), average velocity is $16.8km/hr$.