I worked out the force parallel to the incline if he pushed it down the incline, but cos his force is now parallel to the floor, I'm stuck!!
This is qu 5.9 from 13th edition of Uni Physics Freedman & Young:
A man pushes a piano (180kg) so it has a constant velocity down a ramp inclined at 11.0degrees. Friction is negligible/non-existent for this question. Calculate the magnitude of the force applied by the man if he pushes:
a) parallel to the incline:
b) parallel to the floor:
My answer for part a) is 336.9N
I used W=mg=180*9.81=1765.8N, and this is the weight of the piano.
Then, splitting the force component up using sin and cos, I saw that the force I need is in the sin11degrees direction. Force(push) = Wsin11deg. = 1765.8*sin11deg. = 336.9N
I thought I could work out part b) using (Fcos11)^2 + (Fsin11)^2 = F^2, and rearrange to get Fcos11 = 1733.4N, but this is waaaayyyyy wrong. It looks pretty wrong - the man shouldn't need like 5 times the force if he pushes parallel to the floor.....
Help please?
Merci!!