# Conservation of Energy Problem involving a spring

## Homework Statement

a block is held 1.3m above a spring and is dropped.The spring compresses 6cm before sending the ball into the air. How fast is the ball going when it hits the spring? What is the spring constant? How high in the air does the ball go after hitting the spring?

## The Attempt at a Solution

i can use the following to get the velocity where Y=1.3m and the masses cancel out
M g Y = (1/2) M V^2
To find the k i think i need to use the following equation:
(1/2) M V^2 + M g X = (1/2) kX^2
but i have 2 unknowns M and k iam stuck what to i do?

## Answers and Replies

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tiny-tim
Science Advisor
Homework Helper
…How fast is the ball going when it hits the spring? What is the spring constant?

To find the k i think i need to use the following equation:
(1/2) M V^2 + M g X = (1/2) kX^2
but i have 2 unknowns M and k iam stuck what to i do?
Yup, you're absolutely right … you do need to know the mass of the ball!!

I can only suggest you calculate k as a multiple of M.