A car travels half the distanace with constant velocity ` 30 km //h` and another half with a constant velocity of ` 40 km //h along a straight line. The average velocity of car in km//h is.

Options

A. (a) ` 35`
B. (b) ` 34 .3`
C. (b) `0`
D. (d) ` sqrt(30 xx 40 s`.

Answer

B

Explanation

Here, ` v_1 = 30 km//h. ` v_2 = 40 km//h`
` t-1 = (l//2)/(30) ` and ` t_2 =(l//2) /(40)`
Total tiem ` t= t_1 + t_2 = (l//2) /930) + ( l//2) /(400 = l/2 [ 1/(30) + 1/( 40) ]`
ro ` t = ( 71) /( 2 xx 120)`
Aslo average velocity `= 1/(t-1+ t_2)`
`= (lxx 2400 /( 7l) = ( 240) /7 = 34.3 km//h` .