A man walks on a straight road from his home to a market
2.5 km away with a speed of 5 km/h. Finding the market
closed, he instantly turns and walks back home with a speed
of 7.5 km/h. The average speed of the man over the
interval of time 0 to 40 min. is equal to
a) 5 km/h
b) 6 km/h
c) 30 km/h
45 km/h
Answers
zero to 30min = as the man is moving initially with speed of 5km/hr
in 30 min it will cover 2.5 km i.e he will reach market
average speed = 5km/hr
average velocity = 5km/hr
2) zero to 50 minutes = time taken for reaching back to home = 2.5 km / 7.5 km/hr
= 1/3 hr = 20 min
average speed for 50 min = Total Distance / Total time
= 5 km / 50 min
= 5 x 60 / 50 km/hr
= 6 km/hr
as displacement is zero so average velocity = zero
3)zero to 40 min = Distance travelled in first 30 min = 2.5 km
Distance travelled in next 10 min = 7.5 x 10/60 = 1.25 km
average speed for 40 min = 3.75 km / 40 min
= 3.75 x 60 /40 km/hr
= 5.625 km/hr
Displacement of the man after 40 min = 2.5 - 1.25 = 1.25 km
velocity after 40 min = Displacement/time = 1.25 km/40 min
= 1.25 x 60 /40 km/hr
= 1.875 km/Hr