F5 physics!

淑敏

2011-06-30 3:32 am

in this question ,we shall compare the performance of a battery electric vehicel(BEV) with a petrol vehicle.We assume that the BEV use lead acid batteries.A typical lead acid battery has an energy capacity of 0.8kwh , volume of 7.5X10^-3 m^3,mass of 17kg.Petrol has an energy density of 50MJ kg^-1 and mass density of 700 kg m^-3.

a)the drag force acting on the BEV is 240N at 16ms^-1.Estimate how far the BEV can travel when it is fully charged.
b)find the mass and volume of petrol that provides the same energy as the batteries of 1020kg.

回答 (1)

天同

2011-06-30 4:03 am

✔ 最佳答案

(a) since 1 kWh = 1000 x 3600 J = 3 600 000 J
hence, energy capacity of battery = 0.8 x 3 600 000 J = 2 880 000 J

Power delivered to the car = 240 x 16 w = 3840 w
hence, time the battery power could last = 2880000/3840 s = 750 s
Distance travelled by the car = 16 x 750 m = 12000 m = 12 km

(b) Energy density of battery = 2880000/17 J/kg
Hence, energy produced by 1020 kg of battery
= (2880000/17) x 1020 J = 172 800 000 J = 172.8 MJ

Given the energy density of petrol is 50 MJ/kg
Mass of petrol required = 172.8/50 kg = 3.456 kg
Volume of petrol required = 3.456/700 m^3 = 4.9 x 10^-3 m^2

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