6.2 Friction

A block of mass 1.0 kg rests on a horizontal surface. The frictional coefficients for the block and surface are $\mu_{s} = 0.50$ and $\mu_{k} = 0.40 .$ (a) What is the minimum horizontal force required to move the block? (b) What is the block’s acceleration when this force is applied?

The snowboarder is now moving down a hill with incline $10.0 °$. What is the snowboarder's acceleration?

When you learn to drive, you discover that you need to let up slightly on the brake pedal as you come to a stop or the car will stop with a jerk. Explain this in terms of the relationship between static and kinetic friction.

A physics major is cooking breakfast when she notices that the frictional force between her steel spatula and Teflon frying pan is only 0.200 N. Knowing the coefficient of kinetic friction between the two materials, she quickly calculates the normal force. What is it?

(a) What is the maximum frictional force in the knee joint of a person who supports 66.0 kg of her mass on that knee? (b) During strenuous exercise, it is possible to exert forces to the joints that are easily 10 times greater than the weight being supported. What is the maximum force of friction under such conditions? The frictional forces in joints are relatively small in all circumstances excep…

(a) If half of the weight of a small $1.00 \times 10^{3} -\text{kg}$ utility truck is supported by its two drive wheels, what is the maximum acceleration it can achieve on dry concrete? (b) Will a metal cabinet lying on the wooden bed of the truck slip if it accelerates at this rate? (c) Solve both problems assuming the truck has four-wheel drive.

A machine at a post office sends packages out a chute and down a ramp to be loaded into delivery vehicles. (a) Calculate the acceleration of a box heading down a $10.0 °$ slope, assuming the coefficient of friction for a parcel on waxed wood is 0.100. (b) Find the angle of the slope down which this box could move at a constant velocity. You can neglect air resistance in both parts.

Calculate the maximum acceleration of a car that is heading down a $6.00 °$ slope (one that makes an angle of $6.00 °$ with the horizontal) under the following road conditions. You may assume that the weight of the car is evenly distributed on all four tires and that the coefficient of static friction is involved—that is, the tires are not allowed to slip during the acceleration opposite to the motion. (Ignore…

Repeat the preceding problem for a car with four-wheel drive.