A small block of mass m is kept on a bigger block of mass M which is attached to a vertical spring of spring constant k as shown in the figure. The system oscillates vertically. (a) Find the resultant force on the smaller block when it is displaced through a distance x above its equilibrium position. (b) Find the normal force on the smaller block at this position. When is this force smallest in magnitude? (c) What can be the maximum amplitude with which the two blocks may oscillate together?

a) From the free body diagram

Therefore, resultant force is

b) Normal force R is given by

We know


For R to be smallest,should be max. i.e. x is maximum. The particle should be at the highest point.

c) The two blocks may oscillate together in such a way that. At limiting R=0. Then

So, maximum amplitude is