Work, power & energy Questions and Answers

A 62-kg pole vaulter running at 11 m/s vaults over the bar. Her speed when she is above the bar is 1.3 m/s. Neglect air resistance, as well as any energy absorbed by the pole, and determine her altitude as she crosses the bar.

if an object has 100 joules of potential energy at the top of a ramp How much kinetic energy will there be at the other two places indicated? What assumptions must be made to get these answers, if any? A) 50 joules and 200 joules assuming there is no friction B) 50 joutes and 100 joules with no assumptions needed C) 100 joules and 150 joules assuming there is no friction D) 100 jutes and 150 joules with no assumptions needed

An 8 kg box at rest on the ground is pushed by a force for 12 m. The box ends up going 3 m/s (and there is no friction). A) Ebefore = B) Eafter = C) Does Ebefore = Eafter? D) Put the above information into the Law of Conservation of Energy equation. E) Solve for the force.

Potential (Ep) or Kinetic (E) Energy ___ A car is traveling 45 mph. ___ A rock is on a ledge 5 meters high. ___ A car is resting at the top of a hill. ___ A ball is thrown into the air and is still moving. ___ A ball rolling on the ground.

Circle the one with more Potential Energy A 25 kg mass or a 30 kg mass at the top of a hill? A car at the top of the hill or the bottom of a hill? A plane on the ground or a plane in the air? A full plane or an empty plane (both are flying)?

A 25 kg mass or a 30 kg mass going 5 m/s. Two 10 kg masses, one going 75 m/s, one going 45 m/s. A car at rest or a car rolling down a hill. A heavy bike or a light bike.

A bullet of mass 10 × 10-³ kg moving with a speed of 20ms-¹ hits an ice block (0°c) of 990 g kept at rest on a frictionless floor and gets embedded in it. If ice takes 50% of K.E, for melting, then the mass of the ice block that has melted is(J = 4.2J/Cal ) (Latent heat of ice = 80 cal/g)

A block of ice of mass 50 kg is sliding on a horizontal plane. It starts with speed 5 m/s and stops after moving through some distance. The mass of ice that has melted due to friction between the block and the surface is: [Assuming that no energy is lost and latent heat of fusion of ice is 80 cal/g , J = 4.2 J/cal ] A. 2.86 g B. 3.86 g C. 0.86 g D. 1.86 g

A body of mass 200 g begins to fall from a height where its potential energy is 80 J. Its velocity at a point where kinetic and potential energies are equal is: A. 4 m/s B. 400 m/s C. 20 m/s D. 10√8 m/s

A fixed pulley is driven by a 100kg mass falling at a rate of 8.0m in 4.0s. It lifts a load of 75.0kgf. What is the power input to the pulley taking the force of gravity on 1kg as 10N ? A. 200 W B. 2000 W C. 1000 W D. 1050 W

A magnet of magnetic moment M is lying in a magnetic field of induction B. W₁ is the work done in turning it from 0° to 60° and W2 is the work done in turning it from 30° to 90°. Then A. W2 =W1/2 B. W2 = 2 W1 C. W2 = W1 D. W₂ = √3W₁

A chain of mass m and length / is kept on a table as shown. It is about to move in this position. If it is disturbed slightly then it falls off from table. The total work done by friction is A. -7/32 mgl B. -17/16 mgl C. -9/16 mgl D. -3/32 mgl

Suppose that a block is dropped from rest onto a spring that is oriented vertically. The block falls 1.5 m before landing on the spring (spring constant = 160 N/m) and compressing it 12 m before the block and spring momentarily come to rest. (The spring then pushes the block upward.) What is the mass of the block? Use g= 10 m/s^2. A. 0.66 B. 1 C. 2 D. 8 E. none of these is within 3% of the correct answer.

There is a net force of 50 N exerted on a car that traveled 325 meters. The force is exerted in the same direction of travel. What is the net work done on the car? A. 26 J B. 28 J C. 16,250 J D. 17,500 J

An ice skater in a red jacket is skating south when they collide with, and hold onto, a second skater in a blue jacket who is traveling due east. Just prior to this collision, the person in the blue jacket had a speed of 5 m/s east and the person in the red jacket had a speed of 10 m/s to the south. What is the magnitude of the velocity of the two people immediately after the collision? The mass of skater in the blue jacket is 120 kg and the mass of the skater in the red jacket is 80 kg. A. 11 B. 8 C. 7 D. 5 E. None of these answers is within 3% of the correct answer.

The figure below shows an object with a mass of m= 3.00 kg that starts from rest at point A and slides on a track with negligible friction. Point A is at a height of h = 5.70 m. \(a) What is the object's speed at point B (in m/s)? What is the object's speed at point C (in m/s)? (b) What is the net work (in J) done by the gravitational force on the object as it moves from point A to point C?

A 618-kg elevator starts from rest and moves upward for 3.80 s with constant acceleration until it reaches its cruising speed, 1.83 m/s. (a) What is the average power of the elevator motor during this period? (b) How does this amount of power compare with its power during an upward trip with constant speed? (Give the power during an upward trip with constant speed.)

An ideal spring of negligible mass hangs vertically at equilibrium. You find that if you gently attach a 796-gram mass and allow the spring to stretch very slowly downward, the spring stops and remains at rest when it has stretched 15.3 centimeters from its starting position. What is the value of the spring constant, in newtons/meter?

A 68.5-kg athlete leaps straight up into the air from a trampoline with an initial speed of 8.1 m/s. The goal of this problem is to find the maximum height she attains and her speed at half maximum height. (a) What are the interacting objects and how do they interact? (b) Select the height at which the athlete's speed is 8.1 m/s as y = 0. What is her kinetic energy at this point? What is the gravitational potential energy associated with the lathlete? (c) What is her kinetic energy at maximum height? What is the gravitational potential energy associated with the athlete? (d) Write a general equation for energy conservation in this case and solve for the maximum height. Substitute and obtain a numerical answer. (e) Write the general equation for energy conservation and solve for the velocity at half the maximum height. Substitute and obtain a numerical answer.

A piano with a mass of 126 kg is lifted 10 m above the ground in 4 s by a crane. What is the power used by the crane, measured in watts (W)? Answer: W (round to the nearest whole number)

A 10.0-kg shell is traveling horizontally to the right at 25.0 m/s relative to the ground when it explodes into two fragments, one of mass 3.00 kg and the other of mass 7.00 kg. The lighter fragment goes directly forward, and the explosion releases 1.50 × 103 J of mechanical energy to the fragments. Find the magnitude and direction of the velocity of the heavier fragment relative to the ground just after the explosion. Ignore the effect of any ejected gases.

A shell explodes into two fragments, one fragment 25 times heavier than the other. If any gas from the explosion has negligible mass, then A. the momentum change of the lighter fragment is exactly the same as the momentum change of the heavier fragment. B. the momentum change of the heavier fragment is 25 times as great as the momentum change of the lighter fragment. C. the kinetic energy change of the lighter fragment is 25 times as great as the kinetic energy change of the heavier fragment. D. the kinetic energy change of the heavier fragment is 25 times as great as the kinetic energy change of the lighter fragment. E. the momentum change of the lighter fragment is 25 times as great as the momentum change of the heavier fragment.

A 1.2-kg spring-activated toy bomb slides on a smooth surface along the x-axis with a speed of 0.50 m/s. At the origin 0, the bomb explodes into two fragments. Fragment 1 has a mass of 0.40 kg and a speed of 0.90 m/s along the negative y-axis. In the figure, the energy released by the explosion is closest to A. 0.36 J. B. 0.32 J. C. 0.24 J. D. 0.28 J. OE. 0.20 J.

A 2.9 kg flower pot falls from a window ledge 11.0 meters above the sidewalk. What is the pot's velocity just as it hits the sidewalk? Remember that PE at the top = KE at the bottom! Use 10 m/s² for gravity. Round your answer to the nearest 0.1 (tenths place). Do not add units.

A student with a mass of 65 kg runs up a staircase as shown. What is the work done against gravity? *use 10 m/s² for gravity* A. 780 J B. 455 J C. 7800 J

In which of the following scenarios is NO work being done? Choose all that apply. A. walking VERY slowly up the stairs B. carrying a tissue box C. pushing on a brick wall that moves a single millimeter D. a sloth climbs along a tree branch E. standing on the stairs F. lifting a tissue box G. a squirrel sitting on a tree branch H. pushing on a brick wall that doesn't move

A sled of mass 30.00kg is pulled by a force of 60.00N making an angle of 25.00 degrees with the horizontal direction. The sled moves through a distance of 20.00m. The coefficient of kinetic friction is 0.200. a) How much work is done by the force? b) How muck work is done by the frictional force? c) What is the velocity of the sled?

Dasher and Dancer use 1,349 N of force to pull Santa's sleigh out of the barn, traveling 8.5 meters. If it takes 23.6 seconds, how many watts of power are generated? Round your answer to the nearest 0.1 (tenths place). Do not add units.

A 200 kg boulder rests on a cliff at 1000 m on a mountain side. If the boulder falls then what is the: a. expected kinetic energy just before it impacts with the ground? Final velocity just before it hits the ground?

Two students were climbing stairs at school. Student 1 has a weight of 700 N. Student 2 has a weight of 560 N. If Student 1 climbed the stairs in 5 s and Student 2 beat him with a time of 4 s, who is more powerful and why? A. Student 1 is more powerful, because Student 1 had to overcome more weight force than Student 2. B. Student 2 is more powerful, because Student 2 was faster than Student 1. C. Students 1 and 2 have the same amount of power, because each successfully climbed the 4 meter flight of stairs. D. Students 1 and 2 have the same amount of power, because the quotient of the work divided by time is the same for both.

A 1.45 kg plastic ball is rolling forward at 1.14 m/s. It collides with a second plastic ball of mass 0.94 kg, also rolling forward at 0.47 m/s. After the collision, both balls continue rolling at different speeds. The 1.45 kg ball is now rolling at 1.62 m/s. What is the new velocity of the 0.94 kg ball? Round your answer to the nearest 0.01. Do not add units.

A rifle can shoot a 4.2 g bullet at a speed of 965 m/s. Find the kinetic energy of the bullet. What work is done if the bullet starts from rest? If the work is done over a distance of 0.75 m, what is the average force on the bullet?

A force of 22 N is exerted horizontally on an 18 kg box to move it 7.6 m across the floor. If the box was initially at rest and is now moving at 4.31 m/s calculate the work done. What is the final kinetic energy of the box?

A 0.280 kg block on a vertical spring with a spring constant of 4.66 x 10^3 N/m is pushed downward, compressing the spring 0.0700 m. When released, the block leaves the spring and travels upward vertically. The acceleration of gravity is 9.81m/s2. How high does it rise above the point of release?

A 97.6 N sack of grain is hoisted to a storage room 51 m above the ground floor of a grain elevator. How much work was required? Answer in units of J. part 2 of 3 What is the potential energy of the sack of grain at this height? Answer in units of J. part 3 of 3 The rope being used to lift the sack of grain breaks just as the sack reaches the storage room. What kinetic energy does the sack have just before it strikes the ground floor? Answer in units of J.

Steam to drive an old-fashioned steam locomotive is supplied at a constant gauge pressure of 1.75*106 N/m² (about 250 psi) to a piston with a 0.200-m radius. (a) By calculating P*4V, find the work done by the steam when the piston moves 0.800 m. Note that this is the net work output, since gauge pressure is used. (b) Now find the amount of work by calculating the force exerted times the distance traveled. Is the answer the same as in part (a)?

A 0.0300-kg bullet is fired vertically at 200.0 m/s into a 0.159-kg baseball that is initially at rest. The bullet lodges in the baseball and, after the collision, the baseball/bullet rise to a height of 37.0 m. Assume up to be the positive direction. What was the average force of air resistance while the baseball/bullet was rising? If the force is upward, enter a positive answer and if the force is downward, enter a negative answer.

You use 15 N of force to lift a 2 kg box, then carry the box across a 10 m room. You don't raise or lower the box as you walk. How much work is done on the box as you walk across the room? A. 200 J B. 150 J C. 1500 J D. 20 J E. none - the force applied is perpendicular to the motion

Dasher and Dancer use 1,398 N of force to pull Santa's sleigh out of the barn, traveling 7.9 meters. If it takes 27.6 seconds, how many watts of power are generated? Round your answer to the nearest 0.1 (tenths place). Do not add units.

A pole-vaulter of mass 60.0 kg vaults to a height of 8.10 m before dropping to thick padding placed below to cushion her fall. What is the speed with which she lands on the padding?

Santa's elf needs to move a gift box 6 meters across the room, then 0.5 meters up onto a shelf. Which of the following would require the MOST amount of work? A. lifting the box up 0.25 m, carrying it halfway, setting it down to rest, then picking it up and carrying it to the shelf B. no work is done on the box in any scenario C. all scenarios require the same amount of work D. lifting the box up 0.5 m, then carrying it across the room and placing it on the shelf E. pushing the box 6 m across the floor, then lifting it 0.5 m and placing it on the shelf F. not enough information

A basketball of mass 0.62 kg starts rolling down an incline with an initial velocity of 0.45 m/s. After rolling to the bottom of the incline, you measure the speed of the center of mass to be 1.8 m/s. Calculate the height of the incline. Include the standard Sl unit abbreviation in your answer. Hint: Treat the basketball like a spherical shell.

While decorating, your friend drops a holiday ornament. (Oh no!) Explain using the concepts of impulse and momentum why the ornament is more likely to survive the collision with the ground if it is dropped from a low heigh than it would be from a higher height. (Note: Less force on the ornament would be safer. Assume the time of the collision is the same in both cases.) Include a momentum bar chart for each case along with your reasoning. Your system for the bar charts should be only the ornament, and the scale of your two bar charts should be consistent.

A 52.7 kg student walks up a flight of stairs in 3.88 seconds, traveling a total of 3.1 meters. How many watts of power are generated by the student? *use 10 m/s² for gravity* Round your answer to the nearest 0.1 (tenths place). Do not add units.

Dizzy is speeding along at 24.8 m/s as she approaches the level section of track near the loading dock of the Whizzer roller coaster ride. A braking system abruptly brings the 321-kg car (rider mass included) to a speed of 2.76 m/s over a distance of 5.16 meters. Determine the magnitude of the braking force (in newtons) applied to Dizzy's car.

The length of nylon rope from which a mountain climber is suspended has a force constant of 1.38×10^4 N/m. Given his mass plus the mass of his equipment are 94.3 kg, how much would this rope stretch in centimeters to break the climber's fall if he free-falls 2.08 m before the rope runs out of slack?

A 1.05 kg book falls off a shelf that is 1.16 m high. What is the book's kinetic energy just as it hits the ground? Remember that PE top = KEbottom *Remember to use 10 m/s² for acceleration due to gravity.* Round your answer to the nearest 0.1. Do not add units.

Gravitational potential energy of an object that is lifted off the ground is equal to: (choose all that apply) A. the object's mass times gravity times its height off the ground B. the force used to lift it C. the object's mass times its speed D. the work done to lift it E. the work done divided by the time taken to lift it

A 2.00 kg ball is thrown upward at some unknown angle from the top of a 20.0 m high building. If the initial magnitude of the velocity of the ball is 20.0 m/s. What is the value of total energy? a. 487 J b. 593 J c. 290 J d. 792 J

A ball with mass 0.885 kg and speed 3.9 m/s rolls across a level table into an open box with mass 0.769 kg. The box with the ball inside it then slides across the table for a distance of 0.19 m. The accleration of gravity is 9.81 m/s². What is the coefficient of kinetic friction of the table?