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 40 J.
The potential energy-displacement graph of a 0.5 kg ball moving along a frictionless track is shown in Fig. 7.39. At O, the velocity of the ball is 0 m s-1 and potential energy is 30 J. Calculate the velocity of the ball at P, Q and R.
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According to the potential energy-displacement graph in Fig. 7.39, total mechanical energy is fixed at 30 J. At point P, the graph indicates potential energy is 20 J, leaving 10 J for kinetic energy, which gives a speed of 6.32 m s-1. At point Q, potential energy is 30 J, meaning kinetic energy is 0 J and velocity is 0 m s-1. The ball cannot reach R.
For more NCERT Solutions of Class 9 Science Exploration Chapter 7 Work, Energy and Simple Machines Question Answer (2026-27)
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