Question

An electric car is being designed to have an average power output of 6,500 W for 2 h before needing to be recharged. (Assume there is no wasted energy.) (a) How much energy would be stored in the charged batteries? J (b) The batteries operate on 70 V. What would the current be when they are operating at 6,500 W? A (c) To be able to recharge the batteries in 1 h, how much power would have to be supplied to them? W

Answer 1

Average output power = 6500 W for 2 h

Energy = Power x time

(a) energy would be stored in the charged batteries = 6500 x 2 x 60 x 60 = 468 x 105 J.

(b) The batteries operates on 70 V.

Power = Voltage x current

therefore, current = power / voltage = 6500 / 70 = 650 /7 A.

(c) Total energy required to charge the battery is 468 x 105 J.

Now, as the time is reduced we need more power to store same amount of energy.

Power needed in 1 hr = (468 x 106) / (1 x 60 x 60) = 13,000 W.