Answer:
a)
, b) 
Explanation:
a) Let consider two equations of equilibrium, the first parallel to ski slope and the second perpendicular to that. The equations are, respectively:
The force on the skier is:



b) The equations of equilibrium are the following:

The force on the skier is:



××

×
50N is your force and the acceleration is -9.8m/s^2 due to gravity.
So, you just plug that in.

BUT you know that mass cannot be negative, so you just disregard the negative sign and the mass of the rock is 5.102 grams.
Answer:
216 m
Explanation:
Assuming a straight line:
Δx = vt
Δx = (12 m/s) (18 s)
Δx = 216 m
Energy in a machine can be something technical like a wire or something went wrong with the system