I'm having trouble with numer 3. So work by friction is equal to delta K, which is equal to .5mv^2. So I used the kinematics equation v^2=u^2 + 2ad, where u^2 is the velocity found in number 2 squared. Then I plug in this value of v^2 into the kinetic energy equation to find work, but its not coming up as the right answer. Any ideas? Maybe I'm using the wrong value for acceleration? I've tried many methods for finding a, such as a=u[k]N or a=T/m, but none seem to work.