Friction Warm Up 3

A box is pressed against a wall with an applied force, which of the following equations is correct for the normal force.

• N = W
• N = Fa
• N + W = 0
• N = -Fa

A box is pulled upward at an angle of 35 degrees to the horizontal with a force of 350 N.  Which of the following is the correct expression for the normal force?

• N = W - 350*cos(35)
• N = W + 350*cos(35)
• N = W - 350*sin(35)
• N = W - 350*cos(35)

A ball is rolling across a rough surface with no external forces.  Which of the following is the correct sum of forces acting on the horizontal direction?

• Fa - f_k = 0
• -f_k = ma
• - f_s = 0
• - f_s = ma

A force of 35 N from friction is felt by a box sliding across a rough surface.  Which of the following factors will NOT cause a change in the frictional force felt by the box?

• Increasing its mass
• Changing the surface it is sliding on.
• Increasing its velocity.
• Changing the type of box.

A ball is rolling in the positive direction across a rough surface when a force is applied to it in the negative direction causing it to slow down.  Which of these is the correct sum of forces for the situation?

• Fa + f_s = ma
• -Fa - f_s = ma
• Fa + f_k = 0
• -Fa - f_k = ma