A20kg boy on a 5 kg skateboard coasts to a rest from a speed of 4.5m/s while traveling a distance of 20m on the sidewalk. draw a free body diagram for this situation and calculate the acceleration of the skateboard, the force of friction on the skate board and the coefficient of friction between the skateboard and the sidewalk.

a = -.51 m/s²

coefficient of friction = .05

fk= 12.25 N

Explanation:

mass = 20 + 5kg

weight = 25kg ·9.8 = 245 N

There are many ways to do this I am sure but I did this:

1.  found a by using vf²=vi²-2aΔx. accel is - because it is slowing down.

started at 4.5 m/s, final = 0 and Δx=20....a=-.51 m/s²

2.  the force acting on the object is the friction force which has to equal the mass(accel).

-fk (going to left on free body diagram) = ma

-mu·n = ma

-mu·245N = 25 (-.51)

mu=.05

fk= .05(245N) = 12.25 N

ill do it for 100, also this isnt 80 its 40