An object, previously at rest, slides 5 m5m down a ramp, with an incline of pi/3 π3, and then slides horizontally on the floor for another 2 m2m. If the ramp and floor are made of the same material, what is the material's kinetic friction coefficient?

1 Answer
May 20, 2017

(I really want someone to double check my work since this is one of my first physics answers)

mu_k = 0.9622μk=0.9622

Explanation:

Let's use the top of the ramp for initial condition and bottom of the ramp for final condition.

PE_i + KE_i = PE_f + KE_f + W_"fric"PEi+KEi=PEf+KEf+Wfric

We know that:

Deltay = 5m(sin(pi/3)) = (5sqrt3)/2
KE_i = 0
PE_i = mgDeltay = (5sqrt3mg)/2
PE_f = 0
W_"fric" = 5mu_kF_N = 5mu_kmgcos(pi/3)= 5/2mu_kmgcolor(white)"-"

So our equation becomes:

(5sqrt3mg)/2 = KE_f + 5/2mu_kmg

We can also have another point (f2) at the end of the 2 meters when the block is at rest.

PE_f + KE_f = PE_"f2" + KE_"f2" + W_"fric2"

PE_f, PE_"f2", and KE_"f2" are all 0, and W_"fric2" = 2mu_kmg

KE_f = 2mu_kmg

Substituting this into the first equation gives:

(5sqrt3mg)/2 = 2mu_kmg + 5/2mu_kmg

(5sqrt3)/2 = 9/2mu_k

mu_k = (5sqrt3)/9 = 0.9622

Final Answer