Two massless springs of spring constant $$\mathrm{K}_1$$ and $$\mathrm{K}_2$$ are connected one after the other forming a single chain, suspended vertically and certain mass is attached to the free end. If '$$e_1$$' and '$$e_2$$' are their respective extensions and '$$\mathrm{f}$$' is their stretching force, the total extension produced is

A wooden black of mass '$$\mathrm{m}$$' moves with velocity '$$\mathrm{V}$$' and collides with another block of mass '$$4 \mathrm{~m}$$', which is at rest. After collision the block of mass '$$\mathrm{m}$$' comes to rest. The coefficient of restitution will be

Force is applied to a body of mass $$2 \mathrm{~kg}$$ at rest on a frictionless horizontal surface as shown in the force against time $$(F-t)$$ graph. The speed of the body after 1 second is

A molecule of mass 'm' moving with velocity 'v' makes 5 elastic collisions with a wall of container per second. The change in momentum of the wall per second in 5 collisions will be