From Fig. 7.38, the car maintains a steady speed of 35 m s-1 between A and B. Kinetic energy at A is 612500 J. Braking from B to C performs minus 612500 J of work, generating heat and sound.
A 1000 kg car is moving along a road at a constant speed. Suddenly, the driver notices some obstruction ahead and applies the brakes to come to a complete stop. The graphical representation of motion of the car starting from the instant the driver spots the traffic ahead is shown in Fig. 7.38. (i) Describe how the car moves between positions A and B. (ii) Calculate the kinetic energy of the car at A. (iii) State the work done by the brakes in bringing the car to a halt between B and C. (iv) What does the kinetic energy of the car transform into?
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Using the speed-time graph in Fig. 7.38, the car moves with uniform speed at 35 m s-1 from time 0 to 1 second between A and B. Its kinetic energy at A is half multiplied by 1000 kg multiplied by 35 squared, equaling 612500 J. Between B and C, the brakes bring speed to zero, doing minus 612500 J of work, dissipating energy as heat and sound.
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