- #1

bmoore509

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## Homework Statement

An automobile of mass 3000 kg is driven into a brick wall in a safety test. The bumper behaves like a Hooke’s-law spring. It has an effective spring constant of 6 × 106 N/m, and is observed to compress a distance of 4.23 cm as the car is brought to rest. What was the initial speed of the automobile?

Answer in units of m/s.

## Homework Equations

F=-kx

Ke=(1/2)mv^2

U=(1/2)kx^2

Kf+Uf=Ki+Ui

W=Kf-Ki+Uf-Ui

## The Attempt at a Solution

I'm really not sure where to start. I tried doing KE=U but I know that's not right.