Andrew

Consider a 2.75-W electric clock. 

A.) What is the yearly cost, in dollars, of operating such a clock if the cost of electricity is $0.085 per kW⋅h ? 

A pitcher supplies a power of P = 224 W to a baseball of mass m = 0.075 kg for a period of t = 0.28 s. 

A.) What is the ball's speed in m/s when it leaves his hand? 

A 60.0 kg skier with an initial speed of 17 m/s coasts up a 2.50 m high rise as shown in the figure.

A.) Find her final speed right at the top, in meters per second, given that the coefficient of friction between her skis and the snow is 0.36. 

Suppose the ski patrol lowers a rescue sled carrying an injured skiier, with a combined mass of 82.5 kg, down a 60.0° slope at constant speed, as shown in the Figure. The coefficient of kinetic friction between the sled and the snow is 0.100.

A.) How much work, in joules, is done by friction as the sled moves 29.5 m along the hill? 

B.) How much work, in joules, is done by the rope on the sled over this distance? 

C.) What is the work, in joules, done by the gravitational force on the sled? 

D.) What is the net work done on the sled, in joules? 

A 5.8 × 105 kg subway train is brought to a stop from a speed of 0.55 m/s in 0.45 m by a large spring bumper at the end of its track.

1.) What is the force constant k of the spring in N/m?

 A 22-kg child starts from rest and slides down a slide that is 2.5 m high. At the bottom of the slide, the child is moving 1.91 m/s. 

How much work, in joules, was done by the nonconservative force of friction on the child? 

The thrust produced by a single jet engine creates a force of F = 91000 N. It takes the jet (with a mass of m = 9900 kg) a distance of d = 0.75 km to take off.

A.) What is the take-off speed of the jet vt in m/s? 

B.) How far in meters would you need to depress a giant spring k = 100,000 N/m in order to launch the jet at the same speed without help from the engine? 

A box m = 53 kg is being pulled by a constant force F = 166 N at an angle of θ = 18 degrees. The initial speed of the box is zero. 

A.) Write an expression for the work done by force F as the block moves a horizontal distance d. 

B.) How much work, in joules, was done in moving the block 5.2 m? 

C.) What is the speed of the box at d = 5.2 m if the surface is frictionless? 

 A farmer is using a rope and pulley to lift a bucket of water from the bottom of a well that is hy = 15 m deep. The farmer uses a force F1 = 51.5 N to pull the bucket of water directly upwards. The total mass of the bucket of water is mb + mw = 3.9 kg.

A.) Calculate how much work Wf in J the farmer does on the bucket of water (via the rope) to raise it to ground level. 

B.) Calculate how much work Wg in J gravity does on the bucket filled with water as the farmer lifts it up the well. 

C.) Calculate the net work Wnet in J done on the bucket of water by the two forces F1 and Fg. 

A boy is pulling his sister in a wagon, as shown in the figure. He exerts a force of F = 59.5 N at an angle of 30°.

How much work does the boy do pulling his sister, in joules, if he pulls her 28 m?