A disconcerted dog of a mass 7.80 kg is sliding down a frictionless plank which is inclined at an angle of 48.0 degrees to the horizontal.
Calculate the force which accelerates the dog down the plank.
The force which accelerates the dog is given by
F = mgsin(θ)
less friction, if any.
The force which presses on the plank (hence causes friction) is given by
N = mgcos(θ).
In the case of a frictionless plank, N does not matter.