When you push a 1.92-kg book resting on a tabletop, you have to exert a force of 2.05 N to start the book sliding. Once it is sliding, however, you can use a force of only 1.03 N to keep the book moving with constant speed. What are the coefficients of static and kinetic friction between the book and the tabletop?

A 42.0-kg parachutist is moving straight downward with a speed of 3.85 m/s. (a) If the parachutist comes to rest with constant acceleration over a distance of 0.750 m, what force does the ground exert on her? (b) If the parachutist comes to rest over a shorter distance, is the force exerted by the ground greater than, less than, or the same as in part (a)? Explain.

When you push a 1.80-kg book that is resting on a tabletop, a force of 2.25 N is required to start the book sliding. Once it is sliding, however, a force of only 1.50 N keeps the book moving with constant speed. What are the coefficients of static and kinetic friction between the book and the tabletop?

Wilbur is asking Mr. Ed the talking horse to pull a cart. Mr. Ed replies that he would like to, but the laws of nature just won't allow it. According to Newton's third law, he says, if he pulls on the cart, it pulls back on him with an equal force. Clearly, then, the net force is zero, and the cart will stay put. How should Wilbur answer the clever horse?

A car accelerates at 12 m/s$^{2}$ without spinning the tires. Determine the minimum coefficient of static friction between the tires and the road needed to make this possible.

A 55-kg baseball player slides into third base with an initial speed of 4.6 m/s. If the coefficient of kinetic friction between the player and the ground is 0.46, what is the player's acceleration?

In a daring rescue by helicopter, two men with a combined mass of 172 kg are lifted to safety. (a) If the helicopter lifts the men straight up with constant acceleration, is the tension in the rescue cable greater than, less than, or equal to the combined weight of the men? Explain. (b) Determine the tension in the cable if the men are lifted with a constant acceleration of 1.10 m/s$^{2}$.

When you weigh yourself on good old terra firma (solid ground), your weight is 540 N. In an elevator your apparent weight is 480 N. What are the direction and the magnitude of the elevator's acceleration?

Coffee To Go A person places a cup of coffee on the roof of her car while she dashes back into the house for a forgotten item. When she returns to the car, she hops in and takes off with the coffee cup still on the roof. What is the smallest amount of time in which the person can accelerate the car from rest to $15 \mathrm{~m} / \mathrm{s}$ and still keep the coffee cup on the roof?

A person places a cup of coffee on the roof of her car while she dashes back into the house for a forgotten item. When she returns to the car, she hops in and takes off with the coffee cup still on the roof. (a) If the coefficient of static friction between the coffee cup and the roof of the car is 0.24, what is the maximum acceleration the car can have without causing the cup to slide? Ignore the effects of air resistance. (b) What is the smallest amount of time in which the person can accelerate the car from rest to 15 m/s and still keep the coffee cup on the roof?

You pull your little sister across a flat snowy field on a sled. Your sister plus the sled have a mass of 20 kg. The rope is at an angle of 35 degrees to the ground. You pull a distance of 50 m with a force of 30 N. How much work do you do?

Solve. In one of Leonardo da Vinci’s notebooks, he wrote that “... from the top to the bottom of the chin is the sixth part of a face, and it is the fifty-fourth part of the man.” Suppose the distance from the top to the bottom of the chin of a person in 1.25 in. Using da Vinci’s measurements, find the height of the person.

Coffee To Go A person places a cup of coffee on the roof of her car while she dashes back into the house for a forgotten item. When she returns to the car, she hops in and takes off with the coffee cup still on the roof. If the coefficient of static friction between the coffee cup and the roof of the car is $0.24$, what is the maximum acceleration the car can have without causing the cup to slide? Ignore the effects of air resistance.

Suppose the coefficient of static friction is 0.55 rather than 0.61. (a) Is the weight of the pail and sand necessary to start the pumpkin moving in this case greater than, less than, or equal to 11 N? (b) Calculate the required weight.