Question

Sally applies a total force of 71 N with a rope
to drag a wooden crate of mass 100 kg across
a floor with a constant acceleration in the x-
direction of a = 0.1 m/s2. The rope tied to
the crate is pulled at an angle of  = 50 
relative to the floor.


Calculate the total work done by friction as
the block moves a distance 73.7 m over the
horizontal surface. The acceleration due to
gravity is 9.8 m/s2 .
Answer in units of J

Answer 1

Fap = 71N. @ 50o.

Wc = m*g = 100kg * 9.8N/kg = 980 N. = Wt. of crate.

Fc = 980N. @ 0o. = Force of crate.
Fp = 980*sin(0) = 0 = Force parallel to
floor.
Fv = 980*cos(0) = 980 N. = Force perpendicular to floor.

Fn = Fap*cosA-Fp-Fk = ma.
71*cos50-0-Fk = 100*0.1 = 10
-Fk = 10 - 71*cos50 = -35.63
Fk = 35.63 N.=Force of kinetic friction.

Work = Fk*d = 35.63 * 73.7 = 2700 Joules