Springs

Q.

The change in potential energy, when a body of mass m is raised to a height nR from the earth's surface is
(R = Radius of earth)

1. 

2. 

3. 

4. 

Q. Two wires of the same material (Young's modulus $Y$) and same length $L$ but radii $R$ and $2R$ respectively are joined end to end and a weight $w$ is suspended from the combination as shown in the figure. The elastic potential energy stored in the system is

1. $\frac{3w^{2}L}{4\pi R^{2}Y}$
2. $\frac{3w^{2}L}{8\pi R^{2}Y}$
3. $\frac{5w^{2}L}{8\pi R^{2}Y}$
4. $\frac{w^{2}L}{\pi R^{2}Y}$

Q.

A spring of force constant k is cut into two pieces such that one piece is double the length of the other. Then the long piece will have a force constant of :

1. 

2. 

3. 6k

4. 3k

Q.

When a load is attached to the wire, the ratio of increase in elastic energy of the wire to the decrease in gravitational potential energy when load moves downwards by 1 mm, will be

1. 

2. 

3. 

4. 1