Work, power & energy Questions and Answers

A student wearing frictionless in-line skates on a horizontal surface is pushed by a friend with a constant force of 48 N. How far must the student be pushed, starting from rest, so that her final kinetic energy is 351 J?

A 2.1 kg stone is dropped from a height of 7.6 m and strikes the ground with a speed of 11.5 m/s. What is the magnitude of the average force of air drag that acted on the stone as it fell? 4.1 N 2.3 N 6.2 N 0.73 N 9.3 N

A motor does a total of 480 joules of work in 5.0 seconds to lift a 12-kilogram block to the top of a ramp. The average power developed by the motor is (1) 2400 W (2) 8.0 W (3) 40. W gollos (4) 96 W 10096 199 215 inaben m Os to bet otential Ene

Peter saw Lara Jean running on the school's track field. He accelerates from rest to 8.4 m/s within 26.1 s until he catches up with her. If Peter's mass is 62.05 kg, what is the average power (in hp) dissipated by Peter's body? Round your answer to 2 decimal places.

A 400 hp engine in a 1,600 kg car applies maximum force for 2 seconds to accelerate the car onto the interstate. If the car moves at 8 m/s before accelerating, what is its speed after the 2 seconds of acceleration?

A spring is placed horizontally on a frictionless table. The spring constant of the spring is 50 N/m, and it is compressed 0.1 m by a 2 kg block. a. How much energy is stored in the spring? b. When the spring expands back to its resting position, it pushes the block away. What is the kinetic energy of the block as a result of this force? c. What is the velocity of the block as it is pushed away by the spring?

(8c7p50) A 0.40 kg mass sliding on a horizontal frictionless surface is attached to one end of a horizontal spring (with k = 550 N/m) whose other end is fixed. The mass has a kinetic energy of 15.0 J as it passes through its equilibrium position (the point at which the spring force is zero). At what rate is the spring doing work on the mass as the mass passes through its equilibrium position? 0.00 W Computer's answer now shown above. You are correct. Previous Tries Your receipt no. is 159-4588 At what rate is the spring doing work on the mass when the spring is compressed 0.117 m and the mass is moving away from the equilibrium position? 359.26W Submit Answer Incorrect. Tries 3/8 Previous Tries

If a motor lifts a 400.-kilogram mass a vertical distance of 10. meters in 12.3 seconds, the minimum power generated by the motor is * 3.3 x 10^2 watts 4.9 x 10^3 watts 5.0 x 10^2 watts 3.2 x 10^3 watts

A sled of mass 70 kg starts from rest and slides down a 10° incline 80m long. It then travels for 20 m horizontally before starting back up an 8° incline. It travels 80 m along this incline before coming to rest. What is the magnitude of the net work done on the sled by friction? Round your answer to 2 decimal places. Add your answer

A student, starting from rest, slides down a water slide. On the way down, a kinetic frictional force (a nonconservative force) acts on her. The student has a mass of 76 kg, and the height of the water slide is 12.4 m. If the kinetic frictional force does -6.3 x 103 J of work, how fast is the student going at the bottom of the slide?

The power you need to carry a 1.0-kilogram bag of dog food up a 6.0- meters flight of stairs is 5.5 watts. How long did it take you to accomplish the task? * 11 seconds 8.9 second 33 seconds 1.1 second

A particle is subject to a force Fx that varies with position as shown in the following figure. (a) Find the work done by the force on the particle as it moves from x = 0 to x = 3.00 m. (b) Find the work done by the force on the particle as it moves from x = 5.00 m to x = 6.00 m. (c) Find the work done by the force on the particle as it moves from x = 14.0 m to x = 15.0 m. (d) What is the total work done by the force over the distance x = 0 to x = 15.0 m?

A car is parked at the top of a 64 m -high hill. It slips out of gear and rolls down the hill. How fast will it be going at the bottom?

Which requires more work, stopping a 4.0 kg object moving at 2.0 m/s, or stopping a 2.0 kg object moving at 4.0 m/s? A. Stopping the 4.0 kg object. B. Stopping the 2.0 kg object. C. Both objects require the same work to stop.

A spring with a force constant of 5.0 N/m has a relaxed length of 2.59 m. When a mass is attached to the end of the spring and allowed to come to rest, the vertical length of the spring is 3.86 m. Calculate the elastic potential energy stored in the spring.

The two ropes seen in (Elgure 1) are used to lower a 255 kg plano exactly 4 m from a second-story window to the ground.

To maintain an automobile in approximately constant acceleration, its engine must develop power that increases with time. Suppose that in one situation the work done by an engine is given by W = 7000t² + 60,000t + 100,000 where the units are SI. The power developed by this engine at t = 2 s is

Two identical tiny balls of highly compressed matter are 1.50 m apart. When released in an orbiting space station, they accelerate toward each other at 2.00 cm/s2. What is the mass of each of them? (G = 6.67 10-11 N-m²/kg2)

A baseball is thrown from the outfield toward the catcher. When the ball reaches its highest point, which statement is true? A. Its velocity is not zero, but its acceleration is zero. B. Its velocity and its acceleration are both zero. C. Its velocity is perpendicular to its acceleration. D. Its acceleration depends on the angle at which the ball was thrown. D. None of the above statements are true.

A 2 kg toy car moves at a speed of 5 m/s. a. What is the kinetic energy of the car? b. If a child applies a 3 N force for 2 m in the same direction the car is already moving, how much work is done on the car? c. What is the change in the car's kinetic energy from the applied force? d. What is the final kinetic energy of the car? e. What is the velocity of the car after the child applies the 3 N force?

If the net force applied by the truck ramp in the previous question is -300,000 N, how far along the ramp will the truck move as it stops?

A toy rocket that weighs 10 N blasts straight up from ground level with an initial kinetic energy of 40 J. At the exact top of its trajectory, its total mechanical energy is 140 J. To what vertical height above the ground does it rise, assuming no air resistance? A. 10 m B. 1.0 m C. 24 m D. 14 m

Rita raises a 10kg package to a height of 2.5 m in 2.0 s. (a) How much work did she do on the package? (b) How much power was expended on the package? (c) If she were to raise the package in 1.0 s rather than 2.0 s, how do the work and power change?

A 100%-efficient engine is being used to raise a 89-kg crate vertically upward at a steady rate. If the power output of the engine is 1620 W, how long does it take the engine to lift the crate a vertical distance of 18.7 Friction in the system is negligible.

A spring-loaded dart gun is used to shoot a dart straight up into the air, and the dart reaches a maximum height of 24 meters. The same dart is shot up a second time from the same gun, but this time the spring is compressed only half as far (compared to the first shot). How far up does the dart go this time (neglect all friction and assume the spring is ideal)? A. 6.0 m B. 48 m C. 3.0 m D. 12 m

A roller coaster starting from rest descends 35 meters in its initial drop and then rises 23 meters when it goes over the first hill, which has a circular shape over the top. If a passenger at the top of the hill feels an apparent weight equal to one-half of her normal weight, what is the radius of curvature of the first hill? Neglect any frictional losses.

A sailboat moves north for a distance of 10.00 km when blown by a wind from the exact southeast with a force of 2.00 × 104 N. The sailboat travels the distance in 1.0 h. How much work was done by the wind? What was the wind's power? Your response should include all of your work and a free-body diagram.

A 3.5 kg rock is on a spring launcher pointed vertically into the sky. It has a spring constant of 400 N/m and is compressed by 0.25 m. a. What was the potential energy of the launcher before it was released? b. What is the kinetic energy of the rock just after it was released? c. What is the maximum velocity of the rock? d. What is the gravitational potential energy of the rock at its highest point? e. How high did the rock go?

A frictionless simple pendulum, with a small but dense 4.4-kg mass at the end and a length of 75 cm, is released from rest at an angle of 50° with the vertical. (a) To what height above its lowest point does the mass swing on the other side? (b) What is the speed of the mass at the bottom of the swing?

Stan raises a 1200-N piano a distance of 5.00 m using a set of pulleys. Stan pulls in 20.0 m of rope a. How much effort force would Stan apply if this were an ideal machine? b. What force is used to balance the friction force if the actual effort is 340 N? c. What is the work output? d. What is the input work? e. What is the mechanical advantage?

A Pilgrim uses a block and tackle to lift a 225 N crate a distance of 16.5 m. She pulls 33.0 m of rope with a force of 129 N. What is the ideal mechanical advantage of the machine? 0.50 0.573 1.74 2.00

When you crushed the chalk with a block, you released the 5 kg block from a height of 1 m above the chalk. a. What is the gravitational potential energy of the block-Earth system before you released it? Be sure to mention what you set as your reference level. b. How much kinetic energy did the block have the instant before colliding with the chalk?

A car of mass 1500 kg is at the top of a tall parking structure 24 meters tall. Unfortunately, this car has no engine and must coast to the bottom of the ramp. If the velocity of the car is 12 m/s at the bottom, how much heat was lost during its descent?

A train is traveling at 30.0 m/s relative to the ground in still air. The frequency of the note emitted by the train whistle is 262 Hz. The speed of sound in air should be taken as 344 m/s. What frequency fapproach is heard by a passenger on a train moving at a speed of 18.0 m/s relative to the ground in a direction opposite to the first train and approaching it? What frequency frecede is heard by a passenger on a train moving at a speed of 18.0 m/s relative to the ground in a direction opposite to the first train and receding from it?

A projectile is fired with an initial speed of 36.6 m/s at an angle of 42.2° above the horizontal on a long flat firing range. Determine (a) the maximum height reached by the projectile, (b) the total time in the air, (c) the total horizontal distance covered (that is, the range), and (d) the speed of the projectile 1.50 s after firing.

A driver notices that her 1080-kg car, when in neutral, slows down from 95 km/h to 65 km/h in about 7.0 s on a flat horizontal road. Approximately what power (watts and hp) is needed to keep the car traveling at a constant 80 km/h?

Instead of traditional brakes, a new type of roller coaster is slowed down by a spring. The coaster has 5.0 x 105 J of kinetic energy before it compresses the spring and stops. The spring constant of the spring is 2.0 x 104 N/m. How far is the spring compressed in stopping the roller coaster? What are the system and the initial and final states that you chose for the situation? Include a sketch and bar chart with your solution.

A pop-up toy has a mass of 87.2 g and a spring constant of 57 newtons per meter. A force is applied to the toy to compress the spring 0.025 meters. The toy is activated and all the compressed spring's potential energy is converted to gravitational potential energy. Calculate the maximum vertical height to which the toy is propelled. * What is the total mechanical energy contained within this closed system?

A proton has momentum with magnitude po when its speed is 0.440c. In terms of po, what is the magnitude of the proton's momentum when its speed is doubled to 0.880c?

In a harbor, oil is pumped from the tanks of a ship to a storage tank on land which is 45 m higher in elevation. The total amount of energy spent on to pump 20,000 liters is 7.056 MJ. The oil is pumped for 1 hour. How much power is utilized for pumping 20,000 liters of oil from the ship to the storage tank? 0.118 kW 117.6 W 1.96 W 1.96 kW

The force constant of a spring is 138 N/m. (a) Find the magnitude of the force required to compress the spring by 4.95 cm from its unstretched length. (b) Find the magnitude of the force required to stretch the spring by 7.48 cm from its unstretched length.

Pete Zaria works on weekends at Barnaby's Pizza Parlor. His primary responsibility is to fill drink orders for customers. He fills a pitcher full of Cola, places it on the counter top and gives the 2.6-kg pitcher a 7.8 N forward push over a distance of 36 cm (0.36 m) to send it to a customer at the end of the counter. The coefficient of friction between the pitcher and the counter top is 0.25. Give your answer to the nearest tenth, except for (e) speed, give an answer to the nearest hundredth. a. Determine the work done by Pete on the pitcher during the 36 cm push. b. Determine the work done by friction upon the pitcher. c. Determine the total work done upon the pitcher. d. Determine the kinetic energy of the pitcher when Pete is done pushing it. e. Determine the speed of the pitcher when Pete is done pushing it.

How much work W must be done on a particle with a mass of m to accelerate it from a speed of 0.890 c to a speed of 0.986 c ? Express your answer as a multiple of mc² to three significant figures.

A solid nonconducting sphere of radius 12.0 cm is made of two layers. The innermost section has a radius of 6.0 cm and a uniform charge density of -4.0 C/m³. The outer layer has a uniform charge density of +9.0 C/m³. Determine the electric field for a) 0 <r < 6.0 cm b) 6.0 cm <r < 12.0 cm c) 12.0 cm <r < 50.0 cm d) Plot the electric field for 0 <r < 50.0 cm. Is the field continuous at the edges of the layers?

Roller-coaster car speed using energy conservation. Assuming the height of the hill in Fig. 6-18 is 40 m, and the roller-coaster car starts from rest at the top, calculate (a) the speed of the roller-coaster car at the bottom of the hill, and (b) at what height it will have half this speed. Take y = 0 at the bottom of the hill. APPROACH We use conservation of mechanical energy. We choose point 1 to be where the car starts from rest (v₁ = 0) at the top of the hill (y₁ = 40 m). In part (a), point 2 is the bottom of the hill, which we choose as our reference level, so y₂ = 0. In part (b) we let y₂ be the unknown.

You were tasked with pushing a large box of textbooks across the commons area at Elevation. The box of textbooks have a mass of 23kgs and the total displacement is 75 meters. You manage to complete this task with an acceleration of 0.75 m/s2. How much work did you do?

A 755 N diver drops from a board 10.0 m above the water's surface. Find the mechanical energy of the system, and find the diver's speed 5.00 m above the water's surface. Then find the diver's speed just before striking the water.

A thin flexible uniform chain of mass 'm' and length 'l' is suspended from point 'O' so that its lower end just touches a smooth inelastic fixed plane of inclination 37°. Now the chain is released from point 'O'. Then choose the correct option(s).

You and an elephant are having a sled race down the hill next to the school. You both start at the same height. a. Who has more potential energy? b. Who reaches the bottom of the hill first? c. Who is going the fastest at the bottom of the hill? d. Who has more kinetic energy at the bottom of the hill?

Chemical A. Energy stored in the atom. Nuclear B. Energy stored in molecular bonds. Mechanical C. Caused by friction. Heat. Thermal D. Due to moving electrons. Electrical E. From light. Radiant F. Any kinetic or potential energy.