Question

A particle travels the first half of its total distance along a straight line with a speed 'v'kmph and the next half, with a speed of 60 kmph. If the average speed for the journey is 40 kmph, the value of 'v' is a) 50 kmph b) 30 kmph c) 20 kmph d) 35 kmph ​

Answer 1

c)20kmph

Explanation:

speed of first half total distance ="v"kmph

speed of next half distance =60kmph

the average speed of journey=40kmph

the value of 'v'=60-40=20kmph

v=20kmph

Answer 2

Answer:

b) 30 kmph

Explanation:

given V1 = v , V2 = 60 , average speed = 40

average speed = 2v1v2/V + V2

40= 2v(60)/V+60

40 = 120v/v+60

40v+2400=120v (cross multiplication)

2400=120v-40v

2400=80v

2400/80=v

30=V

so v=30kmph

But, you'll ask if you don't know that how is average speed equal to 2v1v2/ V1+V2,

you can see the proof in the photo.

I'll recommend writing how I got 'v' in your rough for better understanding.

Simple as that.