Question

The odometer of a car reads 57321.0 km when the clock shows the time 08:30 AM. What is the distance moved by the car, if at 08:50 AM, the odometer reading has changed to 57336.0 km? Calculate the speed of the car in km/min during this time. Express the speed in km/h also.
NCERT Solutions for Class 7th Science Chapter 13 Motion and Time Page 156 Exercise Question 5

Answer 1

Initial reading of the odometer of the car = 57321.0 km Final reading of the odometer of the car = 57336.0 km Distance covered by the car = Final reading of the odometer of the car − Initial reading of the odometer of the car = 57336.0 − 57321.0 = 15 km The given car starts at 8:30 a.m. and stops at 8:50 a.m. Therefore, time taken by the car to cover the distance is (8:50 − 8:30) min = 20 min Distance covered by the car = 15 km Time taken by the car = 20 min Apply the formula for speed Speed=distance covered /time taken=15/20=0.75km/m Again, 60 min = 1 h 20 min=1/60×20=1/3hr Time taken by the car =1/3hr Speed=distance covered /ttime taken=15/1/3=45km/hr. Final answer is= 45km/hr

Answer 2

Distance =57336.0km−57321km=15km

Speed in km/min =15km/20min=

4

3

km/min

Speed in km/hr=

4

3

×

min

km

×

hr

60min

=(15×3)km/hr=45km/hr.