A 12-kg crate rests on a horizontal surface and a boy pulls on it with a force that is 30 degree below the horizontal. If the coefficient of static friction is 0.40, the minimum magnitude force he needs to start the crate moving is:

Answer 1

m*g = 12kg * 9.8N/kg = 117.6 N. = Wt. of
the crate.

Fs = u*mg = 0.4 * 117.6 = 47.04 N. =
Force of static friction.

F*cos(-30) - Fs = m*a
0.8669F - 47.04 = m*0 = 0
0.866F = 47.04
F = 54.32 N.

Answer 2

about 71N