Question

A boy runs on a straight road from his home to a market 2.0 km away with a speed of 4 kmph. Finding the market closed, he runs back to his home with a speed of 6kmph. Calculate his (1) average speed (2) magnitude of average velocity (3) average speed of boy in time interval (a) 0 to 30 minute (b) 0 to 40minutes

Answer 1

Answer:

1. 4.8kmph

2. 0kmph

3.(a) 4kmph (b) 4.5kmph

Explanation:

1.

Total Distance(d)=2km+2km=4km

Time required to go to shop= 2/4 hr = 1/2hr

Time required to return= 2/6 hr =1/3hr

Total time(t)=1/2+1/3 =(3+2)/6= 5/6 hr

Avg. speed(s)= total dist./total time=4/(5/6) kmph

=24/5

= 4.8 kmph (Ans.)

2.

Total displacement=0km

Total time=5/6 hr

Avg. Velocity= total displacement/total time

=0/(5/6) kmph

=0 kmph (Ans.)

3.

(a)Time=30min

Distance travelled=2km

Avg. speed= total dist./total time

=2/(1/2) kmph

=4kmph (Ans.)

(b)

Time=40 min

Distance travelled in 30min=2km

Distance travelled in 10 min=6×(10/60)=1km

Total distance =(2+1)km=3km

Avg. speed= total dist./total time

=3/(40/60) kmph

=4.5 kmph (Ans.)