Question

A block of mass m is hanging from the ceiling by a spring whose spring constant is k. Now the spring is pulled further down by x units.

Find the spring force acting on the block at that instant?

• A. mg
• B. kx
• C. k $(\frac{mg}{k}+x)$
• D. None of these

Answer 1

The correct option is C

k $(\frac{mg}{k}+x)$

When you hang the block on the spring, it will be pulled down by block's weight downward and will have extension ${}^{\prime }{x}_0^{\prime }$

Drawing free body diagram

$K{x}_0=mg$

$X_0=\frac{mg}{k}$

Now the spring is pulled down further by x

Total extension in the spring =$x_0+x=(\frac{mg}{k}+x)$

So spring force =$K(\frac{mg}{k}+x)$