Block Sliding, might use work energy theorum

[datrumpet45]

Homework Statement

A block of mass 4.2 kg which has an initial velocity of 3.3 m/s at time t=0, slides on a horizontal surface.

If a constant friction force of 10.2N is exerted on the block by the surface, what is the acceleration?

Homework Equations

Work Energy Theorum?
.5 m v_o² - .5 m v₂²

v = v_o + at

The Attempt at a Solution

I found the kinetic energy of the block, then subtracted the 10.2N of friction. Then I solved for the second velocity. I plugged this into the acceleration equation, but the answer was not correct? Can anyone help me?

 

[gnulinger]

You might be over-thinking this one. What is Newton's Second Law?

 

[genericusrnme]

Using the work energy stuff is going to give you a second order differential equation with 2 boundary conditions to solve (initial and final velocity)
Which is probably a bit harder than is required for this problem..

There is however an equation which relates force to acceleration in a very simple way