Physics
posted by Alex .
A 2.42kg block starts from rest at the top of a 22.9◦ incline and accelerates uniformly down the incline,moving 2.41m in 2.14s. The acceleration of gravity is 9.81m/s2. a) What is the magnitude of the acceleration of the block?
Answer in units of m/s2
b) What is the coeﬃcient of kinetic friction
between the blockand the incline?
c) What is the magnitude of the frictional
force acting onthe block?
Answer in units of N
d)What is the speed of the block after it slides
the distance of 2.41?
Answer in units of m/s

a. you know the final speed (twice average). Vf=2*2.41m/2.14s
Vf^2=Vi^2+2ad solve for acceleration a.
b. do energy concepts
KEfinal=KE initial + PEinitialPEfinalFrictionenergy
or
1/2 m vf^2=0 + mg 2.41/sinTheta 0friction energy
solve for friction energy
then, Frictionenergy=mu(mg*cosTheta)
solve for mu.
c. friction energy=force*distance solve for force.
d. See a. 
Can you tell me the answer for c and d. I got the one for a and b correct but c says it's not correct. I put 21.96N.