A 12-kg crate rests on a horizontal surface and a boy pulls on it with a force that is 30° below the horizontal.If the coefficient of static friction is 0.40, the minimum magnitude force he needs to start the crate moving is:
A)44 N
B)47 N
C)54 N
D)56 N
E)71 N

Question

Quizplus · Accepted Answer

To find the minimum force required to overcome static friction, calculate the normal force and the frictional force. The normal force is reduced by the vertical component of the applied force. The static friction force is the product of the coefficient of static friction and the normal force. Solving for the applied force gives approximately 71 N.

A 12-Kg Crate Rests on a Horizontal Surface and a Boy