Question

A `2kg` block slides on a horizontal floor with the a speed of `4m//s` it strikes a uncompressed spring , and compresses it till the block is motionless . The kinetic friction force is compresses is `15 N` and spring constant is `10000 N//m` . The spring by
A. `5.5 cm`
B. `2.5 cm`
C. `11.0 cm`
D. `8.5 cm`

Answer 1

Correct Answer - A
`W.D_(f) = K_(f) + U_(f) - K_(i) - U_(i)`
`rArr - f.x = (1)/(2)kx^(2) + 0 - (1)/(2)mv^(2) - 0`
`rArr - 15x = 5000 x^(2) - 16 = 0`
`rArr 5000 x^(2) + 15x - 16 = 0 rArr x = 5.5 cm`