Question

A block is suspended by an ideal spring of force constant K. If the block is pulled down by applying a constant force F and if maximum displacement of block from its initial position of rest is δ then

• A.
• B. δ = $\frac { 2 F } { K }$
• C. δ = F/K
• D. Increases in potential energy of the spring is $\frac { 1 } { 2 } K \delta ^ { 2 }$

Answer 1

Answer: (B)

δ = $\frac { 2 F } { K }$

Answer 2

Let mass of the block hanging from the spring be m.

Then initial elongation of the spring will be equal to mg/K. When the force F is applied to pull the block down, then work done by F & further loss of gravitational potential energy of the block is used to increase the potential energy of this spring.

Hence, (F.δ + mg.δ)

= From this equation, δ = , Hence, (2) is the correct choice.