Two blocks A and B are connected to each other by a string and spring , the string passes over a frictionless pulley as shown in fig.1.16 Block B slides over the horizontal top surface of a stationary block C and the block A slides along the vertical side of C, both with the same uniform speed. the coefficient of friction between the surfaces of the blocks is 0.2. THe force constant of the spring is `1960 N.m^-1`. IF the mass of the block A is 2kg, calculate the mass of the block B and the energy stored in the spring.

Explanation

Since the block A is descending with uniform velocity, no normal reaction acts on the block A due to the block C.

Considering the motion of the blocks A and B.
`T=m_Ag=mum_Bg`
`thereforem_B=m_A/mu=2/0.2=10kg`
IF the extension of the spring is x.m, then
`T=kx,or,x=T/k=(m_Ag)/k=(2times9.8)/1960=1/100m`
`therefore` Energy stored in the spring
`=1/2kx^2=1/2times1960times(1/100)^2=0.098J`