Posted by **Ted** on Friday, July 5, 2013 at 11:47am.

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

- Physics -
**Ted**, Friday, July 5, 2013 at 12:07pm
W=mg= 4000 or do i multiply this by 9.81

- Physics -
**MathMate**, Friday, July 5, 2013 at 12:39pm
mg=4000 N is correct.

θ=20°

μ=0.3 (assumed static friction)

Gravity force along plane

F=mg sin(θ)

Friction force along inclined plane

=μmg cos(θ)

direction acts against movement.

To move load up slope:

Force required

=mg sin(θ)+μmg cos(θ)

To move load down slope:

Force required

=μmg cos(θ)-mg sin(θ)

if μmg cos(θ) > mg sin(θ)

=0 otherwise

- Physics -
**Ted**, Friday, July 5, 2013 at 12:52pm
F=4000sin(20)= 1368.1

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

- Physics -
**MathMate**, Friday, July 5, 2013 at 1:30pm
Downward force due to gravity is

F=1368.1

Friction force resisting movement is

FF=1127.6

Therefore net downward force

=force required to prevent load from sliding down

=F-FF

=1368.1-1127.6

=240.45 N

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