5. A car travels from stop A to stop B with a speed of 30 km/h and then returns back to A with a speed of 50 km/h. Find (i) displacement of the car. (ii) distance travelled by the car. (iii) average speed of the car.
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Answer:
37.5 km/hr
Explanation:
Let the distance from A to B be x.
Then displacement of the car when it comes back to the same position is zero.
Distance travelled is 2x.
Time taken by the car when it moves from A to B is given by
t1 = Distance/Speed = x/30
Time taken by the car when it moves from B to A,
t2 = Distance/Speed = x/50
Total distance = 2x
Total time
= t1 + t2
= x/30 + x/50
= (5x + 3x)/150
= 8x/150
So, Average speed
= Total distance/Total time
= 2x/(8x/150)
= 37.5 km/hr
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