10. The kinetic energy of a car is 8 x 10° J as it travels along a horizontal road. How much power is required to stop the car in 10 s? (a) zero watts (c) 8 x 105 w (b) 8 x 104 w (d) 8 x 106 w

A 1680 kg car skids on a level road with coefficient of kinetic friction 0.64 between the tires of the car and the road.  The car skids a distance of 102 m and comes to a complete stop.  The work done on the car by the force of kinetic friction is (enter your answer with two significant figures) possibly useful: W = (Fcosθ)d w = mg g = 9.81 m/s2

88.

You are out on a nice bike ride in the mountains. You and the bicycle together have a mass of 83 kg. Up ahead, there is a huge hill to climb. You stop and drink some water and start to climb. The climb is very hard work. You entertain yourself with your nifty bike computer, which is reporting a power output of 400.0 W! At the end, you've climbed 128 m vertically in 4 minutes and 32 seconds! a) Assuming your power output was constant, how much work did you do during your climb? b) What is the energy transfer equation during this climb? c) Assuming your power output was constant, and no energy was lost, what was your final kinetic energy (remember you started off at rest?

5000 kg dump truck has a maximum 400 hp (1 hp= 746 W), and it is moving up on an inclined road witha slope of 15 degrees. If the frictional coefficient on the road is 0.80, what is the max constant speed that thetrucker can maintain on the inclined?

3. We will now use energy considerations to find the speed of a falling object at impact. Artiom is on the roof replacing some shingles when his 0.55 kg hammer slips out of his hands. The hammer falls 3.67 m to the ground. Neglecting air resistance, the total mechanical energy of the system will remain the same. The sum of the kinetic energy and the gravitational potential energy possessed by the hammer 3.67 m above the ground is equal to the sum of the kinetic energy and the gravitational potential energy of the hammer as it falls. Upon impact, all of the energy is in a kinetic form. The following equation can be used to represent the relationship: GPE + KE = GPE + KE (top) (at impact) Because the hammer is dropped from rest, the KE at the top is equal to zero. Because the hammer is at base level, the height of the hammer is equal to zero; therefore, the PE upon impact is zero. We may write our equation like this: GPE This gives us the equation: (mgh) (top) = KE = (top) = 1/2 mv² (at…

A railroad locomotive accelerates a 95,000-kg railcar from 10 m/s to 25 m/s in 90 seconds. What was the average power transferred to the boxcar during this process? 25 MW 280 kW 330 kW 2.3 MW 48 kW

3

3. a) A 45 g mouse with a kinetic energy of 5.0 J is fleeing a cat. Calculate the speed of the mouse. b) A worker lifts a crate 120 cm vertically. If the lift increases the gravitational potential energy by 97 J, determine the mass of the crate.

A car accelerated from rest to a speed of 20 m/s in a time of 5.6 s. The car has a weight of 9000N. Determine the average power needed to accelerate the car.