Question

A block of mass m is attached with a massless spring of force constant k.The block is placed over a rough inclined surface for which the coefficient of friction is 3/4. The minimum value of M required to move the block up the plane is

Answer 1

Answer:

M=(3/5)m

Explanation:

This can be solved in a better and quicker method using work. Let spring be displaced by a distance x. So M moves by a distance x too. 1/2kx^2=Mgx......equation 1

Now as block moves up ,friction is applied downwards and kx up the plane, Kx=mgsin(theta)+3/4mgcos(theta)

Kx=6mg/5.

Replacing this in equation 1 ,we have

M=3m/5