A car moves for half of its time at 80 kmh-1 and for remaining half at 40 kmh -1 If total distance is 60 km, the average speed of the car is

Question

A car moves for half of its time at 80 kmh-1 and for remaining half at 40 kmh -1 If total distance is 60 km, the average speed of the car is (A) 60 km h-1 (B) 80 km h-1 (C) 120 km h-1 (D) 180 km h-1

Tardigrade Admin · Accepted Answer

upsilonav = ( upsilon1 t1 + upsilon2 t2/t1 + t2) = (80 × (t/2) + 40 × (1/2)/(t)2 + (t)2 i.e. upsilon/av) = ((t/2) (80 + 40)/ (t)2(2)) = (120/2) = 60 km hr-1

Q. A car moves for half of its time at $80 km h^{- 1}$ and for remaining half at $40 km h^{- 1}$ If total distance is $60 km$ , the average speed of the car is

$60 km h^{- 1}$

$80 km h^{- 1}$

$120 km h^{- 1}$

$180 km h^{- 1}$

$υ_{a v} = \frac{υ _{1} t _{1} + υ _{2} t _{2}}{t _{1} + t _{2}}$
= $\frac{80 \times \frac{t}{2} + 40 \times \frac{1}{2}}{\frac{t}{2} + \frac{t}{2}}$
i.e. $υ_{a v} = \frac{\frac{t}{2} ( 80 + 40 )}{\frac{t}{2} ( 2 )} = \frac{120}{2}$
= $60 km h r^{- 1}$

Q. A car moves for half of its time at 80kmh−1 and for remaining half at 40kmh−1 If total distance is 60km, the average speed of the car is

60kmh−1

80kmh−1

120kmh−1

180kmh−1