Question

From what minimum height h must the system be released when a spring is unstretched so that after perfectly inelastic collision (e = 0) with ground, B may be lifted off the ground (spring constant = k).

• A. mg/(4k)
• B. 4mglk
• C. mg/(2k)
• D. None

Answer 1

The correct option is A mg/(4k)

$\Rightarrow 2mgh=\frac{1}{2}k{x}^2$

bw $kx=mg$ For unstretched

$\Rightarrow x=\frac{mg}{k}$

$\Rightarrow 2mgh=\frac{1}{2}\frac{k{m}^2{g}^2}{k^2}$

$\Rightarrow h=\frac{mg}{4k}.$

Hence, the answer is $\frac{mg}{4k}.$