Question

a car covers the first half of thedistance between two places at a speed of40kmph and the second half at 60kmph.calculate the average speed of the car.

Answer 1

Motion

Let the distance between the places = 2d m

So the car covers d m at 40 km/h and other d m at 60 km/h.
So time taken cover d m in 40km/h will be (d/40)h
similarly time taken to cover d m in 60 km/h will be (d/60)km/h

So avg. speed = (Total distance/total time)
$\frac{2d}{ \frac{d }{40} + \frac{d}{60} }$
= {2d/(6d+4d/240)}
= {2d/(10d/240}
= 48 km/hr.

Thats it
Hope it helped
^_^