Reading Fig. 7.39, total energy is 30 J. At P, potential energy is 20 J giving velocity 6.32 m s-1. At Q, potential energy is 30 J giving velocity 0 m s-1. Point R cannot be reached since it requires ...
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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.
The maximum height reached is inversely proportional to acceleration due to gravity. Since the Moon has one-sixth of Earth gravity, the ball travels six times higher, reaching a height of 48 m on the Moon.
From Fig. 7.37, initial speed is 6 m s-1. The trapezoid area gives work done as 150 J, raising kinetic energy to 330 J and final speed to 8.12 m s-1. Acceleration is never negative since force stays positive.
Gravity does negative work upward and positive work downward. Initial kinetic energy is 400 J, while work done by gravity is minus 388 J. The work done by air resistance equals minus 12 J.