Question

What work is said to be done to increase the velocity of a car from 15 km/h to 30 km/h, if the mass of the car is 1000 kg?

Answer 1

m = 1000 kg 

u = 15 km/h = 50/12 m/s

v = 30 km/h = 100/12 m/s

Work done = change in K.E.

K.E. = 1/2 mv² = 1/2 * 1000 * 50/12 * 50/12 = 8680.5 J

K.E. = 1/2 mv² = 1/2 * 1000 * 100/12 * 100/12 = 34722.2 J

34722.2 - 8680.5 = 26041.7 J

Answer 2

The difference between the before- and after- kinetic energy is

(1/2) x (M) x (V22 - V12) = (500 kg) x 3 x (15 km/hr)2 = (1,500 kg) x (15 km/hr)2 =

(1,500kg) x (15 km/hr x 1,000m/km x 1 hr/3,600 sec)2 = (1,500 kg) x (41/6m/sec)2 =

6,250 joules

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