A block of `4kg` mass starts at rest and slides a distance `d` down a friction less incline ( angle `30^@`) where it runs into a spring of negligible mass. The block slides an additional `25m` before it is brought to rest momentarily by compressing the spring. The force constant of the spring is `400Nm^-1`. The value of `d` is (take `g=10ms^-2`)

Options

A. (a) `25cm`
B. (b) `37.5cm`
C. (c) `62.5cm`
D. (d) None of the above

Answer

B

Explanation

`W_(gravity)=DeltaU_(spri ng)`
`mg sin theta(d +0.25)=1/2k(0.25)^2`
which gives `d=37.5cm`