How can I solve this?

Question

At one particular moment, a 19.0 kg toboggan is moving over a horizontal surface of snow at 4.10 m/s. After 9.00 s have elapsed, the toboggan stops. Use a momentum approach to find the magnitude of the average friction force (in N) acting on the toboggan while it was moving.



 _____ N

Answer 1

vi = 4.1 m/s

vf = 0

Δv = vf - vi = 0 - 4.1 = -4.1 m/s

Δ momentum mΔv = (19 kg)(-4.1 m/s) = 77.9 kgm/s

The average friction force (Ff) takes 9 seconds to bring the toboggan to a stop, so impulse = Ft = Ff(9)

Impulse is equal to Δ momentum, so Ff(9) = 77.9;

Ff = 8.66 N