Work, power & energy Questions and Answers

The kinetic friction force between a 60.0-kg object and a horizontal surface is 42.0 N. If the initial speed of the object is 24.0 m/s, and friction is the only force acting on the object, what distance will it slide before coming to a stop?

At a playground, a 20 kg child plays on a slide that drops through a height of 2.5 m. The child starts at rest at the top of the slide. On the way down, the slide does a nonconservative work of -361 J on the child. What is the child's speed at the bottom of the slide?

In the sport of skeleton a participant jumps onto a sled (known as a skeleton) and proceeds to slide down an icy track, belly down and head first. In the 2010 Winter Olympics, the track had sixteen turns and dropped 126 m in elevation from top to bottom. (a) In the absence of nonconservative forces, such as friction and air resistance, what would be the speed of a rider at the bottom of the track? Assume that the speed at the beginning of the run is relatively small and can be ignored. (b) In reality, the gold-medal winner (Canadian Jon Montgomery) reached the bottom in one heat with a speed of 40.5 m/s (about 91 mi/h). How much work was done on him and his sled (assuming a total mass of 118 kg) by nonconservative forces during this heat?

George is riding a roller coaster that starts at a height of 46 m and goes down into a valley that is at ground level. He then goes up a second hill that is 32 m height and goes into a second valley that is 14.5m above the ground. What is George's velocity at the bottom of the first valley, top of the second hill and at the bottom of the second valley?

With what minimum speed must you toss a 200 g ball straight up to just touch the 14-m-high roof of the gymnasium if you release the ball 1.6 m above the ground? Solve this probler using energy. With what speed does the ball hit the ground?

What height does a frictionless playground slide need so that a 35 kg child reaches the bottom at a speed of 4.7 m/s?

A basketball player makes a jump shot. The 0.600-kg ball is released at a height of 2.19 m above the floor with a speed of 7.36 m/s. The ball goes through the net 3.10 m above the floor at a speed of 4.09 m/s. What is the work done on the ball by air resistance, a nonconservative force?

A student places her 440 g physics book on a frictionless table. She pushes the book against a spring, compressing the spring by 6.10 cm, then releases the book. What is the book's speed as it slides away? The spring constant is 1800 N/m.

In a hydroelectric dam, water falls 35.0 m and then spins a turbine to generate electricity. Suppose the dam is 80% efficient at converting the water's potential energy to electrical energy. How many kilograms of water must pass through the turbines each second to generate 45.0 MW of electricity? This is a typical value for a small hydroelectric dam.

7.80-9 bullet moving at 500 m/s penetrates a tree trunk to a depth of 4.70 cm. (a) Use work and energy considerations to find the average frictional force that stops the bullet. (0) Assuming the frictional force is constant, determine how much time elapses between the moment the bullet enters the tree and the moment it stops moving.

A 7.80-g bullet moving at 500 m/s penetrates a tree trunk to a depth of 4.70 cm. (a) Use work and energy considerations to find the average frictional force that stops the bullet. (b) Assuming the frictional force is constant, determine how much time elapses between the moment the bullet enters the tree and the moment it stops moving.

After driving a portion of the route, the taptap is fully loaded with a total of 27 people including the driver, with an average mass of 61 kg per person. In addition, there are three 15-kg goats, five 3-kg chickens, and a total of 25 kg of bananas on their way to the market. Assume that the springs have somehow not yet compressed to their maximum amount. How much are the springs compressed? Enter the compression numerically in meters using two significant figures.

A 63-kg skier (with gear) goes down a 500 meter slope which makes a 16 degree angle with horizontal. They start with zero velocity. a. What is the gravitational potential energy the skier begins with? (500 meters is not the height) b. If there is no friction or air resistance, what would their velocity be when they reach the bottom of the hill? C. If friction and drag together remove energy from the skier by applying 50 N of force during the entire trip, how much energy is removed? d. In this case with friction/drag in part c, what would the skier's velocity be when they reach the bottom of the hill?

A 65 kg softball player slides into second base, generating 550 J of thermal energy in her legs and the ground. How fast was she running?

How much energy is consumed by a 1.0 kW hair dryer used for 11 min? How much energy is consumed by a 12 W night light left on for 17 hr?

A 3.25-kg block of silver is dropped from rest at a height of 75.0 meters. One-third of the potential energy is converted into hear energy which raises the temperature of the silver. The specific heat of silver is 234 joules per kilogram per Celsius degree. What is the increase in temperature of silver? (a) 1.05 Cº (b) 2.32 C* (c) 3.14 Cº (d) 3.73 Cº

How much work does an elevator motor do to lift a 2000 kg elevator a height of 180 m ? How much power must the motor supply to do this in 49 s at constant speed?

A horizontal rope with 15 N tension drags a 25 kg box 6.5 m to the left across a horizontal surface. How much work is done by tension? How much work is done by gravity?

A box is pushed across a rough horizontal floor by a force acting parallel to the floor in the direction of motion. A force doing negative work on the body is A. gravity. B. friction. C. the applied force. D. the normal reaction force of floor upward on body. E. a fictitious force.

Show that the kinetic energy of a particle of mass m is related to the magnitude of the momentum p of that particle by KE = p²/2m. (Note: This expression is invalid for particles traveling at speeds near that of light.) (Submit a file with a maximum size of 1 MB.)

A frog of 0.15-kg mass jumps from the ground up to a height of 0.55 m. How much gravitational potential energy is involved in this jump? Here, the value of the acceleration of gravity is considered to be g = 10 m/s² A. 0.1 Joule. B. 1.0 Joule. C. 0.825 Joule. D. 10 Joule. E. None of the above.

A string of length 'L' and force constant 'K' is stretched to obtain extension 'I'. It is further stretched to obtain extension '1'. The work done in second stretching is 1/2Kl₁ (21 +1₁) 1/2 Kl1² 1/2K(l²+l12) 1/2K(l1² - l²)

Two particles A and B having different masses are projected from a tower with same speed. A is projected vertically upward and B vertically downward. On reaching the ground: velocity of A is grater than that of B velocity of B is greater than that of A both A and B attain the same velocity the particle with the larger mass attains higher velocity

An electric water heater consumes 6.38 kW for 3.85 h per day. What is the cost (in dollars per year) of running it for one year if electricity costs 12.6 cents/(kWh)?

The principle of conservation of energy implies that the amount of energy remains the same during a physical process. In this experiment energy after is less than energy before. This contradicts the principle. Explain.

You have a battery with voltage 8.85 V that you hook up to a single resistor. You measure a current of 0.509 Amps passing through the resistor. What is the power dissipated by the resistor? Make sure to put your answer in an appropriate number of significant figures. Also include units (and these are case sensitive units of n and N are not the same).

A block of mass m = 3.20 kg is pushed a distance d = 5.70 m along a frictionless horizontal table by a constant applied force of magnitude F = 16.0 N directed at an angle 0 = 22.0° below the horizontal as shown in the figure below. (a) Determine the work done on the block by the applied force. (b) Determine the work done on the block by the normal force exerted by the table. (c) Determine the work done on the block by the force of gravity. (d) Determine the work done by the net force on the block.

230-kg block along a horizontal track has a speed of 1.40 m/s immediately before colliding with a light spring of force constant 4.45 N/m located at the end of the track. (a) What is the spring's maximum compression if the track is frictionless? (b) If the track is not frictionless, would the spring's maximum compression be greater than, less than, or equal to the value obtained in part (a)? greater less equal

The chin-up is one exercise that can be used to strengthen the biceps muscle. This muscle can exert a force of approximately 800 N as it contracts a distance of 7.8 cm in a 76-kg male. How much work can the biceps muscles (one in each arm) perform in a single contraction? Your response differs from the correct answer by more than 10%. Double check your calculations. J Calculate the amount of energy required to lift a 76-kg person 40 cm in performing a chin-up. Do you think the biceps muscle is the only muscle involved in performing a chin-up?

A package with a mass of 45.0 kg slides down a smooth ramp with negligible friction. The package starts from rest and has a speed of 2.20 m/s at the bottom. What is the height of the ramp (in m)?

You push a 67 kg box across a floor where the coefficient of kinetic friction is µ= 0.55. The force you exert is horizontal. How much power is needed to push the box at a speed of 0.60 m/s ? Express your answer using two significant figures.

Force F₁ does 5 J of work in 10 seconds, force F2 does 3 J of work in 5 seconds, force F3 does 6 J of work in 18 seconds, and force F4 does 25 J of work in 125 seconds. Rank these forces in order of increasing power they produce. Rank forces from largest power they produse to smallest. To rank items as equivalent, overlap them.

If the lift has a length of 3050 m and makes an angle of 13.5° with the horizontal, what is the change in the gravitational potential energy of the skier- Earth system? Express your answer to three significant figures and include appropriate units.

A 70 kg bicyclist rides his 9.8 kg bicycle with a speed of 13 m/s. You may want to review How much work must be done by the brakes to bring the bike and rider to a stop? Express your answer using two significant figures.

An object of mass m is at rest at the top of a smooth slope of height h and length L. The coefficient of kinetic friction between the object and the surface, , is small enough that the object will slide down the slope if given a very small push to get it started. Part B Review Constants Sam, whose mass is 71 kg, stands at the top of a 10-m-high, 120-m-long snow- covered slope. His skis have a coefficient of kinetic friction on snow of 0.07. If he uses his poles to get started, then glides down, what is his speed at the bottom?

Emily exerts a force of 30 N on the paint- ing in the direction she travels as she first carries it 15 m on a level sidewalk and then climbs 1.5 m up the stairs. Her walk takes 15 s. How much work does Emily do on the painting in all?

James helps his dad put the 250-Newton lawn mower in the back of his dad's truck. They lift the mower up from the ground to the truck bed, which is 3.1 meters above the ground. How much work do James and his dad do?

After hitting a long fly ball that goes over the right fielder's head and lands in the outfield, the batter decides to keep going past second base and try for third base. The 63 kg player begins sliding 3.40 m from the base with a speed of 4.35 m/s. If the player comes to rest at third base. What was the coefficient of kinetic friction between the player and the ground?

Initially sliding with a speed of 4.5 m/s, a 2.0 kg block collides with a spring and compresses it 0.27 m before coming to rest. What is the force constant of the spring? Express your answer using two significant figures.

A 67-kg base runner begins his slide into second base when he is moving at a speed of 3.7 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? (b) How far does he slide?

A 59.5-kg runner has a speed of 3.40 m/s at one instant during a long-distance event. (a) What is the runner's kinetic energy at this instant? (b) If he doubles his speed to reach the finish line, by what factor does his kinetic energy change?

A weight lifter lifts a 360-N set of weights from ground level to a position over his head, a vertical distance of 2.10 m. How much work does the weight lifter do, assuming he moves the weights at constant speed?

If the kinetic energy of a particle is quintuple, by what factor has its speed increased?

A block of mass m slides from rest down a frictionless inclined plane that has a height, h, as shown. The speed, v, of the block at the bottom of the plane in terms of g and his (a) 2gh (b) √2gh (c) √2gh (d) gh

Consider lifting a box of mass m to a height h using two different methods: lifting the box directly or lifting the box using a pulley (as in the previous part). What is W₁/Wp, the ratio of the work done lifting the box directly to the work done lifting the box with a pulley?

If you pull for a half hour or a whole hour on a wagon but it doesn't move, Select one: O a. it is impossible to determine how much work is done. O b. twice as much work is done during the half hour. O C. no work is done in either case. O d. half as much work is done during the half hour.

A logger drags a heavy log across level ground by attaching a cable from the log to a bulldozer. The cable is inclined upward from horizontal at an angle of 20°. The cable exerts a constant force of 2000 N while pulling the log 16 m. How much work is done in dragging the log? 3.0 x 104 J

A 1.0-kg mass is fired from a compressed horizontal spring (k = 1.0 X 103 N/m) across a frictionless floor and up a frictionless ramp. If the initial compression of the spring was 10.0 cm, what maximum height h above the floor will the mass achieve as it slides up the ramp? a. 0.51 m O b. 0.10 m O c. none of these O d. 0.32 m Oe. 0.15 m

A 25-kg crate is dragged across a level floor for a distance of 10 m by a constant horizontal force of 100 N. The amount of work done by the gravity force is a. 5000 J b. 500 J c. 2500 J Od.0J Oe. 1000 J

An object with charge q = -5.00x10-9 C is placed in a region of uniform electric field and is released from rest at point A. After the charge has moved to point B, 0.500 m to the right, it has kinetic energy 3.00×10-7 J. Part A If the electric potential at point A is +30.0 V, what is the electric potential at point B? Express your answer with the appropriate units. VB = Submit Part B HA Value Request Answer Units What is the magnitude of the electric field? Express your answer with the appropriate units. ?