A steel ball of mass 5 g is thrown downward with velocity 10 m/s from height 19.5m. It penetrates sand by 50 cm. The change in mechanical energy will be: (g = 10 m/s2).
Correct answer: B. 1.25J
- A. 1J
- B. 1.25J
- C. 1.5J
- D. l.75J
Explanation
Mass, m = 5g = 0.005 Kgh = 19.5 mx = 50 cm = 0.5 mv = 10 m/sThe change in the mechanical energy, ΔU = mg(h+x) + (1/2)mv2= 0.005 x 10(19.5 + 0.5) + (1/2)x 0.005 x (10)2= 0.005 x 10 x 20 + (1/2)x 0.005 x 100= 1 + 0.25 = 1.25 J
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The work-energy theorem states that the net work done on an object equals its change in kinetic energy. Questions involve positive and negative work, variable forces and force-displacement graphs, acceleration or deceleration, and the difference between this theorem and conservation of mechanical energy, which also requires attention to potential energy and non-conservative work.
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