Friction

Static Friction is present only when an object is at rest.

• True.

• False.

A block is pulled along a rough level surface at constant speed by the force . The figure shows the free-body diagram for the block. F_N represents the normal force on the block; and f represents the force of kinetic friction. What is the magnitude of F_N?

• P

• f

• 2mg

• mg

Tags

NGSS.HS-PS2-1

A 27.6 kg block is pulled along a rough level surface at constant velocity by the force . The figure shows the free-body diagram for the block. F_N represents the normal force on the block; and f represents the force of kinetic friction. The coefficient of kinetic friction is 0.30, what is the strength of P?

• 4.0 N

• 81 N

• 270 N

• 27.6 N

Tags

NGSS.HS-PS2-1

A 2.0-N force acts horizontally on a 10-N block that is initially at rest on a horizontal surface. The coefficient of static friction between the block and the surface is 0.50.What is the magnitude of the frictional force that acts on the block?

• 5 N

• 8 N

• 2 N

• 0 N

Tags

NGSS.HS-PS2-1

A 2.0-N rock slides on a frictionless inclined plane. Which one of the following statements is true concerning the normal force that the plane exerts on the rock?

• The normal force is 2.0 N

• The normal force is greater than 2.0 N

• The normal force is less than 2 N, but greater than 0 N

• The normal force is 0 N.

Tags

NGSS.HS-PS2-1

Under what condition(s) will an object be in equilibrium? (Hint: An object can be in static equilibrium or dynamic equilibrium).

• Only if the object is at rest can it be in equilibrium.

• If the object is either moving with constant velocity or with constant acceleration, it is in equilibrium.

• Only if the object is moving with constant acceleration can it be in equilibrium.

• If the object is either at rest or moving with constant velocity, it is in equilibrium.

A block of mass M is held motionless on a frictionless inclined plane by means of a string attached to a vertical wall as shown in the drawing. What is the magnitude of the tension in the string?

• Mg

• Mg tan 𝜃

• Mg sin 𝜃

Tags

NGSS.HS-PS2-1

• 6.34 N

• 10.0 N

• 3.70 N

• 0 N

Tags

NGSS.HS-PS2-1

A 10-kg block is pushed against a vertical wall by a horizontal force of 100 N as shown in the figure. The coefficient of static friction, 𝜇_s, between the block and the wall is 0.60; and the coefficient of kinetic friction, 𝜇_k, is 0.40. Which one of the following statements is true, if the block is initially at rest?

• The block will slide down the wall because the force of static friction can be no larger than 60 N.

• The block will slide down the wall because the coefficient of kinetic friction is less than the coefficient of static friction.

• The block will remain at rest because the coefficient of static friction is greater than the coefficient of kinetic friction. 

• The total force exerted on the block by the wall is directed horizontally.

Tags

NGSS.HS-PS2-1

At a playground, a child (m=30.0 kg) slides down a slide that makes a 42° angle with the horizontal direction. The coefficient of kinetic friction for the child sliding on the slide is 0.20. What is the magnitude of her acceleration during her sliding?

• 4.6 m/s²

• 9.8 m/s²

• 5.1 m/s²

• 6.4 m/s²

Tags

NGSS.HS-PS2-1