posted by Ted .
A 4000N block is moved up a slope that is 20 degrees to the horizontal. If the coefficient of friction is 0.3, find the force parallel to the slope to: a) move the load up the slope b) prevent the load from sliding back
W=mg= 4000 or do i multiply this by 9.81
mg=4000 N is correct.
μ=0.3 (assumed static friction)
Gravity force along plane
Friction force along inclined plane
direction acts against movement.
To move load up slope:
=mg sin(θ)+μmg cos(θ)
To move load down slope:
=μmg cos(θ)-mg sin(θ)
if μmg cos(θ) > mg sin(θ)
FF= 0.3*4000cos(20)= 1127.6
FR= 4000sin(20) + 0.3*4000cos(20)= 2495.7
So 2495.7 N required to move it up the slope
1127.6 N is required to prevent the load from sliding back
Downward force due to gravity is
Friction force resisting movement is
Therefore net downward force
=force required to prevent load from sliding down