Work, power & energy Questions and Answers

A 2.75-g copper coin at 17.5°C drops 40.0 m to the ground. (a) Assuming 55.0% of the change in gravitational potential energy of the coin-Earth system goes into increasing the Internal energy of the coin, determine the coin's final temperature. (b) Does the result depend on the mass of the coin? Yes No

A block of mass 3.80 kg is placed against a horizontal spring of constant k = 805 N/m and pushed so the spring compresses by 0.0650 m. (a) What is the elastic potential energy of the block-spring system (in J)? (b) If the block is now released and the surface is frictionless, calculate the block's speed (in m/s) after leaving the spring.

A monkey carries a coconut of mass 0.9 kg to a height of 4.6 m. Calculate the potential energy of the coconut and the work done by the monkey against the force of gravity in getting the coconut to that height. Here, the value of the acceleration of gravity is considered to be g = 10 m/s² A. 5 J B. 196 J C. 19.6 J D. None of the above.

A 164 g mass lying on a frictionless table is attached to a horizontal spring with a spring constant of 364 N/m. The spring is stretched a distance of 79 cm (0.79 m). (a) What is the initial potential energy of the system? (b) What is the kinetic energy of the system when the mass returns to the equilibrium position after being released?

A 150 lb (667 N) diver needs to get to the top of a 10 m high diving board. Which method of getting to the top would require the most amount of work? Running up a 40 m inclined plane All of the choices require the same amount of work Climbing a 10 m ladder Walking up a 30 m long ramp

A girl with 40kg mass is riding an 8 kg bicycle. At the top of the hill her speed is 6.0 m/s, and her speed triples at the bottom of the hill. The hill is 15.0 m high. What is the work done by the forces? non-conservative

A 0.2 kg mass is dropped from a 10 m high building on top of a spring that is placed vertically. It stops after moving 9.2 meters down and stops 0.8 meters above the ground while compressing the spring by 0.5 meters. What is the spring constant if air resistance is negligible?

A worker pulls a wagon along the horizontal surface. Weight of the wagon is 80N and the worker exerts 90N force at an angle of 20° above the horizontal for a distance of 12.0 m. a) How much work is done by worker? b) How much work is done by the Normal force? c) How much work is done by friction force if the coefficient of kinetic friction is 0.20?

A spring is attached to the ceiling and pulled 5 cm down from equilibrium and released. After 3 seconds the amplitude has decreased to 4 cm. The spring oscillates 10 times each second. Assume that the amplitude is decreasing exponentially. Find an equation for the distance, D the end of the spring is below equilibrium in terms of seconds, t.

A 0.15-kg baseball approaches the bat traveling to the right at 40 m/s and leaves the bat traveling left at 60 m/s. If the ball is in contact with the bat for 0.3 s, the average force from the bat on the ball is 10 N to the right 10 N to the left 50 N to the left 30 N to the right 50 N to the right

A wind turbine works by slowing the air that passes its blades and converting much of the extracted kinetic energy to electric energy. A large wind turbine has 45-m-radius blades. In typical conditions, 86,000 kg of air moves past the blades every second. If the air is moving at 12 m/s before it passes the blades and the wind turbine extracts 40% of this kinetic energy, how much energy is extracted every second?

A 79 kg bike racer climbs a 1400-m-long section of road that has a slope of 4.3°. By how much does his gravitational potential energy change during this climb?

180 students sit in an auditorium listening to a physics lecture. Because they are thinking hard, each is using 125 W of metabolic power, slightly more than they would use at rest. An air conditioner with a COP of 5.0 is being used to keep the room at a constant temperature. What minimum electric power must be used to operate the air conditioner?

Mark pushes his broken car 190 m down the block to his friend's house. He has to exert a 150 N horizontal force to push the car at a constant speed. How much thermal energy is created in the tires and road during this short trip?

A child with mass m = 15.8 kg slides down a slide 4.99 m high, and reaches the bottom with a speed of 4.43 m/s. How much thermal energy (in Joules) was generated in the process?

How much work does an elevator motor do to lift a 1300 kg elevator a height of 100 m ?

A 0.44 kg object travels from point A to point B. If the speed of the object at point A is 3.0 m/s and the kinetic energy at point B is 8.0 J, determine the following. (a) the kinetic energy (in J) of the object at point A (b) the speed (in m/s) of the object at point B

An electrical power station uses 1.53 x 10^14 J of heat input with an efficiency of 26.2%. (a) How much work is done? (b) How much waste heat is produced by the station? (c) What is the ratio of waste heat to work output?

In a Broadway performance, an 77.0-kg actor swings from a R = 3.70-m-long cable that is horizontal when he starts. At the bottom of his arc, he picks up his 55.0-kg costar in an inelastic collision. What maximum height do they reach after their upward swing? m

The electric motor of a model train accelerates the train from rest to 0.700 m/s in 29.0 ms. The total mass of the train is 635 g. Find the average power delivered to the train during its acceleration. W

A 74-kg base runner begins his slide into second base when he is moving at a speed of 4.1 m/s. The coefficient of friction between his clothes and Earth is 0.70. He slides so that his speed is zero just as he reaches the base. (a) How much mechanical energy is lost due to friction acting on the runner? J (b) How far does he slide? m

A bungee jumper jumps from a high bridge 100 m above a river. How fast does he fall after he has covered 60 m after jumping from the bridge? (Ignore air resistance in the fall.) 28.56 m/s 30.30 m/s 34.29 m/s 18.60 m/s

At what speed should a ball of mass 200 g be rolled in order to reach the other side of a slope, 10 m high? 12 m/s 13 m/s 14 m/s 15 m/s

Look at the picture. Sam applied a force parallel to the ramp to move 25 kg of sand to the top of the ramp. The ramp is 15 m long and 3.0 m high. What is the ideal mechanical advantage of the ramp? Note: Ignore the friction between the ramp and the wheelbarrow. 2 5 6 3

Now that you know how to calculate kinetic energy, you can figure out whether the bus or the baseball has more energy. Remember, the bus has a speed of 1.3 m/s and a mass of 12,000 kg. The baseball has a speed of 44.7 m/s and a mass of 0.145 kg. Calculate the energies below. Bus or Baseball? What is the kinetic energy of the bus? 12,000 J 10,140 J 20,280 J 7800 J

A 340 kg piano slides 2.7 m down a 24 incline and is kept from accelerating by a man who is pushing back on it parallel to the incline (see the figure (Figure 1)). Ignore friction. Determine the force exerted by the man. Determine the work done on the piano by the man. Express your answer to two significant figures and include the appropriate units. Determine the work done on the piano by the force of gravity. Express your answer to two significant figures and include the appropriate units.

A ball is attached to a string that is 1.5 m long. It is spun so that it completes two full rotations every second. What is the centripetal acceleration felt by the ball? (Remember that the length of each rotation is just the circumference of the circle.) 75 m/sec^2 521 m/sec^2 237 m/sec^2 150 m/sec^2

When the car is on the horizontal track after being launched, how fast is the car moving? m/s A spring loaded toy car launcher is made with a spring constant of 101 N/m. When the car, with a mass of 0.18 kg, is placed in the launcher, the spring is compressed a distance of 0.15 meters. The car is launched along a horizontal frictionless track. How much energy is stored in the spring when the car is placed in the launcher? How high up the ramp will the car travel? meters At the end of the horizontal track is a vertical ramp. Assuming the bottom of the ramp is the zero of gravitational potential energy, how much gravitational potential energy will the car have when it reaches its highest point on the ramp? J

A cheetah with a mass of 58 kg, is initially running only 6 m/s. The cheetah sees and begins to chase a tasty antelope, accelerating to a final velocity of 29.3 m/s, during a time interval of 2.8 seconds. What is the initial kinetic energy of the cheetah? What is the final kinetic energy of the cheetah? How much work does the cheetah perform while accelerating? What power output does the cheetah produce while accelerating?

A sledder has 458 J of potential energy and 102 J of kinetic energy at one point on a steep hill. How much kinetic energy will the sledder have at the bottom of the hill? Answer:

If you push a cart three times as far while applying the same force, you do Select one: a. the same amount of work. b. half as much work. c. three times as much work. d. one-third as much work.

A skier with a mass of 83 kg has a speed of 11.1 m/s on a hilltop. The skier then goes down the hill with a vertical drop of 10.1 meters. What is the skier's kinetic energy on top of the hill? What is the skier's kinetic energy at the bottom of the hill? How fast is the skier moving after reaching the bottom of the vertical drop? How much work did gravity do on the skier as the skier went down the hill?

Calculate the kinetic energy of a particle with a mass of 3.34 x 10-27 kilogram and a speed of 2.89 × 105 meters per second.

A boulder rolls from the top of a mountain, travels across a valley below, and rolls part way up the ridge on the opposite side. Describe all the energy transformations taking place during these events and identify when they happen A. As the boulder rolls down the mountainside, KE is converted to PE. As the boulder rolls up the opposite slope, KE is converted to PE. The boulder rolls only part way up the ridge because some of the PE has been converted to thermal energy due to friction. B. As the boulder rolls down the mountainside, KE is converted to PE. As the boulder rolls up the opposite slope, PE is converted to KE. The boulder rolls only part way up the ridge because some of the PE has been converted to thermal energy due to friction. C. As the boulder rolls down the mountainside, PE is converted to KE. As the boulder rolls up the opposite slope, KE is converted to PE. The boulder rolls only part way up the ridge because some of the PE has been converted to thermal energy due to friction. D. As the boulder rolls down the mountainside, PE is converted to KE. As the boulder rolls up the opposite slope, PE is converted to KE. The boulder rolls only part way up the ridge because some of the PE has been converted to thermal energy due to friction.

Ned (40kg) and Ed(54kg) are twins. Ned runs up stairs (6m high) in 3 s while Ed walks up the same stairs in 7s. Who did more work? Ed did less work because it took him more time to travel the 6m of vertical height. Neither twin did any work. Ed did more work because he has more mass and travelled the same distance as Ned.

Which state summarizes the Law of Conservation of Momentum? * Matter can neither be created nor destroyed. The total momentum in a system stays the same before and after an interaction. Every action has an equal and opposite reaction.

At the bottom of its swing, a Pendulum has a kinetic energy of 3 J. What is the potential energy for the pendulum at the top of the swing?

A spring does 5.0 J of work on a 0.10-kg ball bearing in a pinball machine. The ball's resulting speed just after leaving the spring is .5 m/s 1 m/s 5 m/s 10 m/s

An electric motor attached to a pickup truck is used to rescue and lift a climber out of a canyon. If it lifts the climber 10.20 m in 18.0 s by exerting an upward force of 18900 N. What power does the motor produce in kilowatts (kW)?

A 20-kg box is lifted with a constant velocity through a height change of +4 m and then held in place. How much work is done on the box DURING the lift? * a. 200 J b. 800 J c. 3200 J d. 0 J

A box with a mass 2 kg is sliding along on a friction-free surface at 9.87 m/s at a height of 1.81 m. It travels down the hill and then up another hill. Find the initial kinetic energy. Find the initial potential energy.

(6) A 20-kg box is lifted with a constant velocity through a height change of +4 m and then held in place. How much work is done on the box AFTER the lift while held in place? * a. 200 J b. 800 J c. 3200 J d. 0 J

A woman pushing a box exerts 9.87 N*m worth of of work on it, how much energy does she transfer to the box if she pushes the box 5 meters? Round your answer to the nearest 10th's place.

A roller coaster car of mass 1500-kg starts from rest at an elevation of 35.0 m high and rolls down and then up another incline of lower height 18.0 m. (a) How much potential energy does the roller coaster have at the starting position? (b) How much kinetic energy does the roller coaster have at the starting position? (c) Find the total energy of the roller coaster. (d) How much potential energy does the coaster have at the lower elevation? (e) How much kinetic energy does the coaster have at the lower elevation? (f) How fast is the coaster traveling?

A 5.0 kg block is at rest on a horizontal rough surface. It is now pushed up against a spring (k = 300 N/m) and the spring is compressed a horizontal distance of 0.35 m. The spring is now released and the block is allowed to slide in a straight-line path across the rough surface until it comes to rest. If the coefficient of kinetic friction between the block and the surface μk = 0.15, how far will the block slide until it comes to rest?

Jeff is part of a trekking team. As he climbs a hill, he drops his water bottle, which has a mass of 0.25 kilograms. The bottle slides down the hill and is moving at a velocity of 14 meters/second the instant it hits the ground. The vertical height from where Jeff dropped the bottle is? Ignore friction, and use K.E=1/2mv² ,P.E=m*g*h, and g=9.8m/s²

Paul and Ivan are riding a tandem bike together. They're moving at a speed of 5 meters/second. Paul and Ivan each have a mass of 50 kilograms. What can Paul do to increase the bike's kinetic energy? А. He can let Ivan off at the next stop. B. He can pedal harder to increase the rate to 10 meters/second. C. He can reduce the speed to 3 meters/second. D. He can pick up a third rider.

Using your calculation in question 2, calculate how long it would take this person to burn a 250-Calorie iced mocha, (Remember: 1 Calorie = 4184 J) Mass: 70 kg, Height of Stairs: 4.5 m, Time1: 3.82s , Time2: 3.82s, Time3: 3.70 s

An object that is in motion has mechanical energy potential energy kinetic energy acceleration

A 2.5 hp (1 hp = 744 W) motor is used to power a hoist to lift a 1700 kg car 1.86 m above the garage floor. a)How much time does it take the hoist to lift the car? b)The hoist slowly lowers the car back down to the ground. How much work does the hoist motor do in lowering the car?