JEE Main · 2007 · 29 Apr 2007 · Offline · Laws of Motion

A block of mass '

m

' is connected to another block of mass '

M

' by a spring (massless) of spring constant '

k

'. The blocks are kept on a smooth horizontal plane. Initially the blocks are at rest and the spring is unstretched. Then a constant force '

F

' starts acting on the block of mass '

M

' to pull it. Find the force on the block of mass '

m

Answer: (C)

Solution

With the surface smooth, the applied force accelerates both blocks together, so the common acceleration is

a = \frac{F}{m + M}

. The only horizontal force acting on the block of mass

m

is the spring force, and it must supply exactly this acceleration. Hence the force on that block is

ma = \frac{m F}{m + M}

JEE Main · 2007 · 29 Apr 2007 · Offline · Single correct option