**1. The problem statement, all variables and given/known data**

A block moves along a frictionless surface with an initial velocity of 10 m/s. It contacts a spring of spring constant 350 N/m. Underneath the spring at and after the point of contact the ground is rough and applies a constant friction force of 45 N. The spring compresses 0.75 m before the mass stops. What is the mass of the block?

**2. Relevant equations**

Ki + Ui = Kf + Uf

**3. The attempt at a solution**

Ui and Kf are zero, so I had 1/2mv^{2} = 45 + 1/2kx^{2}, but I’m not sure where to put the friction force in the equation.

The answer is supposed to be 2.64 kg… Please help!

http://ift.tt/PlNdGE