Work Energy and...

A stone of mass $$1\ kg$$ is tied of the end of a string $$1\ m$$ long. It is whirled in a vertical circle. If the velocity of stone at the top is $$4\ m/s$$. What is the tension in the string at the lowest point? 

A massive ball moving with a speed $$v$$ collide with a tiny ball having a very small mass , immediately after the impact the second ball will move at speed approximately equal to :

A spring of spring constant $$5\times 10^3N/m$$ is stretched initially by 5 cm from the unstretched position. Then the work required to stretch it further by another 5 cm is

Name the type of energy (kinetic energy $$K$$ or potential energy $$U$$) possessed in the following case.

A particle moves under the effect of a force $$F=cx$$ from $$x=0$$ to $$x=x_1$$, the work done in the process is

Name the type of energy (kinetic energy $$K$$ or potential energy $$U$$) possessed in the following case.

Two solid rubber balls $$A$$ and $$B$$ having masses $$200\ \&\ 400\ \text{gm}$$ respectively are moving in opposite direction with velocity of $$A$$ equal to $$0.3\ \text{m/sec}.$$ After collision the two balls come to rest when the velocity of $$B$$ is :

A man raises a box of mass $$50 \ kg$$ to a height of $$2 \ m$$ in $$2 \ minutes$$, while another man raises the same box to the same height in $$5 \ minutes$$. What is the ratio of work done by them ?

A spring of force constant $$800\ N/m$$ has an extension of $$5\ cm$$. The work done in extending it from $$5\ cm$$ to $$15\ cm$$ is