(iii) What is the velocity of the ball just before it lands on the ground, after falling from the height of 40 m?
(iv) The ball bounces to a height of far less than 40 m, indicating it has lost much of its energy when bouncing.What happens to the energy lost by the ball?
(i) Given that the pendulum bob has a mass of 50 g, calculate its potential energy while at this position. (9)
(ii) Calculate the maximum velocity of the bob. (7) (iii) Describe an experiment to demonstrate an energy conversion. (12)
(c) A 3 500 kg pile driver is used to drive a metal stake into the ground. It takes the motor 20 s to raise the pile drive 8 m. Upon striking the stake it applies an average force of 4.5 105 N as it drives the stake 40 cm into the ground.
Calculate: (i) the work done by the motor to raise the pile driver (6) (ii) the power output of the motor. (6)
(iii) If the pile driver’s motor operates at 20 kW, what is the efficiency of the motor? (6)
(iv) How much work is done on the metal stake? (6)
(v) Why is there a difference in the kinetic energy of the pile drive as it hits the stake compared with the amount of work done on the stake? (4)
A pile driver at work Fig 5.3
(3) (4)
(b) A simple pendulum, of length 80 cm, was set up as illustrated in Fig 5.3 so that the string made an angle of 60 to the vertical. (Acceleration due to gravity 9.8 m s2.)
