Work Energy and Power

Practice Questions:

Question 11: easy

A simple pendulum is released from A as shown. If m and l represent the mass of the bob and length of the pendulum, the gain in kinetic energy at B is

1. mgl/2

2. mgl/√2

3. 2mgl/√3

4. √3mgl/2

View Answer

From Principal of conservation of Energy in absence of non-conservative forces,

Ui+ Ki= Uf+ Kf

⇒ Ui- Uf= Kf - Ki

⇒ Loss in Potential Energy = Gain in Kinetic Energy

⇒ Gain in Kinetic Energy = m.g. l .cos 30° = √3mgl/2

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Question 12: easy

If potential energy between electron and proton at a distance r is given by U =-(ke²/3r³), then force acting is

1. F = ke²/r²

4. F = ke²/r

View Answer

Force F = - dU/dr = d ((ke²/3r³))/dr = ke²/r^4

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Question 13: easy

The potential energy of a particle varies with distance x as shown in the graph :

The force acting on the particle is zero at

1. C

2. B

3. B and C

4. A and D

View Answer

For Equilibrium dU/dx =0 so, Points of maxima and minima in U-x graph are point of equilibrium.

So, Points B and C are equilibrium positions

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