A girl drove to hospital from her home the odometer reading of car increased by 12 kilometre if the trip took 18 minute then -
a) what was her average speed?
b) if she returned home by the same path in 2 hour 12 minute what was her average speed for the entire trip?
c) what was her displacement and total distance travelled by her?
d) convert your answer of average velocity in kilometre per hour , metre per minute , metre per second , centimetre per second .
Answers
a) Distance travelled by girl = 12 km = 12 × 1000 = 12000 m
And time taken to cover that = 18 min = 18 × 60 = 1080 seconds
Now,
Average speed = Distance/Time
= 12000/1080 = 11.11 m/sec
OR
Distance = 12 km and time = 18 min = 18/60 = 0.3 hours
Average speed = 12/0.3 = 40 km/hr
b) Return time by girl = 2 hours 12 minutes
Total time = 2 hours 12 minutes + 18 minutes = 2 hours 30 minutes = 2.5 hours
The girl returns to her home at the same distance. So, the distance is the same i.e. 12 km
Total distance = 12 + 12 = 24 km
Average speed = Distance/Time
= 24/2.5 = 9.6 km/hr
c) Total Displacement by girl is zero. Because the point from where she starts, she returns to the same point. Means, starting and ending points are the same.
Total distance = (12 + 12)km = 24 km
d) For part (a)
Average velocity in km/hr = 40 km/hr
In m/min = 666.67 m/min
In m/sec = 11.11 m/sec
In cm/sec = 1111.11 cm/sec
For part (b)
Average velocity in km/hr = 9.6 km/hr
In m/min = 160 m/min
In m/sec = 2.67 m/sec
In cm/sec = 266.67 cm/sec
Given:-
The odometer reading is 12 km and time taken is 18 minutes.
To find:-
a) what was her average speed?
b) if she returned home by the same path in 2 hour 12 minute what was her average speed for the entire trip?
c) what was her displacement and total distance travelled by her?
d) convert your answer of average velocity in kilometre per hour , metre per minute , metre per second , centimetre per second .
Solution:-
a) 18 minutes = 18/60 hours = 3/10 hours
Distance = 12 km
Time = 3/10 hours
Speed = Distance/Time
= 12/(3/10)
= 40 km/h
b) Time taken in her return trip = 2 hours 12 minutes
= 2 hours 12/60 hours
= 2 hours 1/5 hours
= 2 + 2.2 hours
= 2.2 hrs
Time taken to reach home = 3/10 hours
Total time = 2.2 + 0.3
= 2.5 hours
Total distance = 12 + 12 km = 24 km
Average speed of the whole trip = 24/2.5
= 9.6 km/h
c) Her displacement = 0 m
(Because she ends in the same point where she started from, i.e. from the hospital)
Total distance travelled by her = 12 + 12 = 24 km
d) Average velocity of the whole trip = 9.6 km/h (from b)
9.6 km/h = 9.6*16.667
= 160 m/min
9.6 km/h = 9.6 / 3.6
= 2.67 m/s
9.6 km/h = 9.6*27.778
= 266.67 cm/s