Question

A 2 kg block is dropped from 45 cm above a spring. If the spring compresses 5 cm what was its initial velocity??

Answer 1

as block dropped from 45 cm initially it's velocity would be 0.

Answer 2

if u know the spring constant use\[mgh=.5mv^2+.5kx^2\]

Answer 3

or else use the kinematics

Answer 4

I think you need to know the spring constant for this.

At the point where the mass stops moving it has fallen 50cm
The loss of PE is therefore given by mgh which you can calculate.
The mass had an initial vertical velocity and hence an initial KE (0.5 mv^2)

SO once it has come to rest the total loss of energy is mgh + 0.5mv^2
This must be equal to the energy stored in the spring.


The spring absorbs energy = 0.5 kx^2, but unless you know k you cannot calculate this.

Check your question to see if you have the spring constant given...

@ksaimouli seems to hint at an alternative method ??kinematics?? but I can't see a way to a solution unless you have k