posted by tharidu on .
While trying to decide where to hang a framed picture, you press it against the wall to keep it from falling. The picture weighs 5.0 N and you press against the frame with a force of 6.0 N at an angle of 40 ° from the vertical. (a) What is the direction of the normal force exerted on the picture by your hand? (b) What is the direction of the normal force exerted on the picture by the wall? (c) What is the coefficient of static friction between the wall and the picture? The frictional force exerted on the picture by the wall can have two possible directions. Explain why.
a. Perpendicular to and toward the frame and wall.
b. Opposite direction of normal force exerted by hand.
c. A = 90 - 40 = 50 Deg., CCW.
Fv = 5 + 6*sin50 = 9.60 N. = Normal.
Fn = Fap - u*Fv = 0.
6*cos(50) - u*9.6 = 0.
9.6u = 6*cos(50) = 3.86.
u = 3.86 / 9.6 = 0.402.
If the picture was placed on the opposite wall, the angle would be:
A = 90 + 40 = 130 Deg.
The cosine would be negative and the
coefficdient of friction and force ot
friction would be in opposite direction.