(i) A battery lights a bulb. Describe the energy changes involved in the process.
(ii) Calculate the amount of work needed to stop a car of 500 kg moving at a speed of 36 km
(i) When a battery lights a bulb, its chemical energy changes into light and heat energy.
(ii) Here, m = 500 kg, v = 0 and
u =36 km = 36 x 100/ 3600 = 10m
Work done = Change in kinetic energy = 1/2 m ( ${{v}^{2}}$ - ${{u}^{2}}$) = 1/2 x 500 ( 0 - 10 x 10)
= -1/2 x 500 x 100 = -25000 ${{Js}^{-1}}$
So, it is negative because work is done to stop the car.