Calculating Work on a Sliding Block: Mass, Speed, and Kinematics

[coolcalx]

Homework Statement

A block of mass 3 kg, which has an initial
speed of 6 m/s at time t = 0, slides on a
horizontal surface.
Find the magnitude of the work that must
be done on the block to bring it to rest.
Answer in units of J.

Homework Equations

F=MA
W=FD
Kinematics
Vf=Vi=AT
ΔX=ViT=1/2AT²
2AΔX=Vf²-Vi²

The Attempt at a Solution

basically I need A and ΔX(D)... and I can't remember what to do. after that, it's a simple matter of plugging in numbers

 

[rock.freak667]

Hint: The change in kinetic energy is the same as the work done on the block.

 

[coolcalx]

yeah, ha, totally forgot about the other formula xD