Unit 4 - ENERGY A 130 kg ball is sliding along a homemade roller coaster at a height of 90 cm and with a speed of 0.35 m/s. PLEASE sketch a simple diagram. a) Calculate its kinetic energy and gravitational potential energy at 90 cm b) with what maximum speed could it reach the ground? c) If the roller coaster is 700% efficient, what would the actual speed be at the bottom?

Physics Review A team of huskies performs 7 440 J of work on a loaded sled of mass 124 kg, drawing it from rest up a 4.60-m high snow-covered rise while the sled loses 1 520 J due to friction, (a) What is the net work done on the sled by the huskies and friction? (b) What is the change in the sleds potential energy? (c) What is the speed of the sled at the top of the rise? (See Section 5.5.)

Suppose a car travels 108 km at a speed of 30.0 m/s, and uses 2.0 gal of gasoline. Only 30 of the gasoline goes into useful work by the force that keeps the car moving at constant speed despite friction. (The energy content of gasoline is about 140 Mi/gal.) (a) What is the magnitude of the force exerted to keep the car moving at constant speed? (b) If the required force is directly proportional to speed, how many gallons will be used to drive 108 km at a speed of 28.0 m/s?

“ E=K+Uconstant is a special case of the work energy theorem.” Discuss this statement.

In the Back to the Future movies (https://openstaxcollege.org/l/2lbactofutclip), a DeLorean car of mass 1230 kg travels at 88 miles per hour to venture back to the future. (a) What is the kinetic energy of the DeLorean? (b) What spring constant would be needed to stop this DeLorean in a distance of 0.1m?

Suppose a car travels 108 km at a speed of 30.0 m/s, and uses 2.0 gal of gasoline. Only 30% of the gasoline goes into useful work by the force that keeps the car moving at constant speed despite friction. (See Table 7.1 for the energy content of gasoline.) (a) What is the magnitude of the force exerted to keep the car moving at constant speed? (b) If the required force is directly proportional to speed, how many gallons will be used to drive 108 km at a speed of 28.0 m/s?

Give an example of a situation in which there is a force and a displacement, but the force does no work. Explain why it does no work.

A 100 — kg man is skiing across level ground at a speed of 8.0 m/s when he comes to the small slope 1.8 m higher than ground level shown in the following figure. (a) If the skier coasts up the bill, what is his speed when he reaches the top plateau? Assume friction between the snow and skis is negligible. (b) What is his speed when he reaches the upper level if an 80 — N frictional force acts on the skis?

One person drops a ball from the top of a building while another person at the bottom observes its motion. Will these two people agree (a) on the value of the gravitational potential energy of the ball-Earth system? (b) On the change in potential energy? (c) On the kinetic energy of the ball at some point in its motion?

A block of mass m = 1.62 kg slides down a frictionless incline (Figure 2-A). The block is released a height h = 3.91 m above the bottom of the loop. What is the force of the inclined track on the block at the bottom (point A)? What is the force of the track on the block at point B? At what speed does the block leave the track? How far away from point A does the block land on level ground? Sketch the potential energy U(x) of the block. Indicate the total energy on the sketch. FIGURE 2-A Problem 2-25.