Physics Problem Kinetic co-efficient and distance.?

Question

The problem states that a school bus pulls into an intersection as a car approaches at 25 km/h on an icy street. as the car's driver sees the bus 26 m away, he slams on the brakes and since the car does not have anti-lock breaks, it slides towards the intersection. I am given a co-efficient of kinetic friction that equals 0.10 and I am asked if the car hits the bus. The answer key states that the car stops after traveling 24.6 m and does not hit the bus, but without the car's mass or weight, I am not sure how to proceed. Is there something that I am missing?

Answer 1

you don't need the mass. However, you need to get it cancel out.
Fweigh=mg
Fnormal=mg

Friction=u(Fnormal)
Friction=u(mg)

a=Fnet/m
since friction make up Fnet, we have:
a= u(mg) / m
the mass cancel out.
a= ug
a= .98m/s^2 (should be -.98m/s^2 because of friction)

Vf^2=2ad+Vi^2
0=2(-.98)d+6.94^2
-48.22=-19.6d
d=24.6m

Answer 2

The car's mass cancels out...

Ffric = coeff * m * g
Ffric = .1m(9.8)

Newton's second law says Forces Fwd - Forces backward = ma

So 0 - .1m(9.8) = ma

M divides out and gives you an acceleration of -0.98 m/s/s

Then you can use the formula Vf^2 - Vo^2 = 2 a d

Convert 25 km/hr to m/s... 25km/hr *1000m/km * 1 hr/3600s = 6.94 m/s


0 - (6.94)^2 = 2(-.98) D and solve for D....