7. Friction, Inclines, Systems

A block $1$ rests on a horizontal surface and is connected by a light string over a frictionless pulley to a hanging block $2$. If block $2$ is heavier and tends to pull block $1$ to the right, in which direction does the static friction force act on block $1$?

Which of the following best describes the difference between $f\_\mathrm{static}$ (static friction) and $f\_\mathrm{kinetic}$ (kinetic friction)?

When you walk across a carpet and then touch a metal object, you often feel a shock. Which of the following best explains this phenomenon in terms of static friction?

Which type of friction is generally more difficult to overcome when starting to move an object at rest on a surface?

A block of mass $m$ rests on an inclined plane that makes an angle $\theta$ with the horizontal. What is the minimum coefficient of static friction required to prevent the block from sliding down the plane?

Which type of friction acts on an object that is not moving?

Which of the following is an example of a static friction process?

A crate rests on a horizontal floor. If the coefficient of static friction between the crate and the floor is $\mu s_{}$ = $0.5$, what is the maximum possible static friction force that can act on a $20$ kg crate before it starts to move? (Assume $g$ = $9.8$ ms-2.)

A cyclist is riding on a flat road and needs to make a turn of radius $r$ at a constant speed $v$ without skidding. What is the minimum possible coefficient of static friction between the bike tires and the ground required to safely make the turn?

A pickup truck is carrying a toolbox, but the rear gate of the truck is missing. The toolbox will slide out if it is set moving. The coefficients of kinetic friction and static friction between the box and the level bed of the truck are $0.355$ and $0.650$, respectively. Starting from rest, what is the shortest time this truck could accelerate uniformly to $30.0$ m/s without causing the box to slide? Draw a free-body diagram of the toolbox.

Why do clothes often cling together after tumbling in a clothes dryer?

A 36N force is needed to start a 7.0 kg box moving across the floor. If the 36.0 N force continues, the box accelerates at 0.70 m/s². What are the coefficients of static and kinetic friction?

A box of bananas weighing $40.0$ N rests on a horizontal surface. The coefficient of static friction between the box and the surface is $0.40$, and the coefficient of kinetic friction is $0.20$. What minimum horizontal force must the monkey apply to start the box in motion?

A box of bananas weighing $40.0$ N rests on a horizontal surface. The coefficient of static friction between the box and the surface is $0.40$, and the coefficient of kinetic friction is $0.20$. What is the magnitude of the friction force if a monkey applies a horizontal force of $6.0$ N to the box and the box is initially at rest?

A box of bananas weighing $40.0$ N rests on a horizontal surface. The coefficient of static friction between the box and the surface is $0.40$, and the coefficient of kinetic friction is $0.20$. If no horizontal force is applied to the box and the box is at rest, how large is the friction force exerted on it?