When a car spends two hours driving at 20 km/h, and then an hour driving at 50 km/h. then the average speed of the car would be 30 km/h , therefore the correct answer is option D.
What is speed?
The total distance covered by any object per unit of time is known as speed. It depends only on the magnitude of the moving object. The unit of speed is meter/second. The generally considered unit for speed is a meter per second.
The mathematical expression for speed is given by
average speed = total distance /Total time
As given in the problem A car spends two hours driving at 20 km/h, and then an hour driving at 50 km/h
The total distance covered by the car is
S =2×20 +1×50
=90 km
The total time taken by the car is
T = 3 hour
then by using the formula for the average speed
average speed = total distance /Total time
By substituting the respective values of the total speed and total time
average speed = 90/3 km/h
=30 km/h
Thus, The correct answer is option D because a car's average speed would be 30 km/h if it spent two hours traveling at 20 km/h and one hour traveling at 50 km/h.
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