A car moving over a straight path, covers a distance d with constant speed of 40 km/hr and then the same distance with speed 60km/hr. The average speed of car is .....

Options

A. 50 km/hr
B. 48 km/hr
C. 52 km/hr
D. None of the given

Answer

B

Explanation

To cover distance d with constant speed 40 km /hr,
Time `t_(1) = (d)/(40) hr.`
And to cover distance d with constant speed 60 km/hr required time `t _(2) = (d)/(60) hr.`
`therefore ` Total time required to cover distance 2d is
`t = t _(1) +t _(2)`
`therefore t = (60 d )/(40) + (d)/(60)`
`therefore t = (60 d + 40 d )/(2400)`
`therefore t = (d)/(24)`
Now average velocity `bar v = (2d)/(t) = 2d xx (24)/(d) = 48 Km//hr`