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Exam 10: Energy and Work

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Question 1

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4.00 × 10⁵ J of work are done on a 1110 kg car while it accelerates from 10.0 m/s to some final velocity.Find this final velocity.

A) 28.6 m/s
B) 22.9 m/s
C) 25.7 m/s
D) 31.5 m/s

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Question 2

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Find the net work done by friction between the ground and the body of a snake slithering in a complete circle of 3.93 m radius.The coefficient of friction between the ground and the snake is 0.25,and the snake's weight is 54.0 N.

A) 330 J
B) 0 J
C) 3300 J
D) 670 J

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Question 3

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A person drops one rock from rest and it falls 100 meters down a cliff before hitting the ground.The person then throws an identical rock downward.The amount of kinetic energy gained by the rock dropped from rest is _____ that of the second rock,and the magnitude of the change in speed (between hitting the ground and its initial speed) of the rock dropped from rest is _____ that of the second rock.

Particle 1 has the mass of Particle 2,yet they both have the same kinetic energy.Compare the momenta of two particles.

A 2.3 kg object moving at 7.3 m/s collides inelastically with a 4.0 kg object which is initially at rest.What percentage of the initial kinetic energy of the system is lost during the collision?

A child swings on a ball of mass m on a rope in a uniform,vertical circle of radius r at a constant speed v.How much work is done by the centripetal force on the ball during one complete revolution?

A block starts from rest at the top of a 31.0° inclined plane and encounters a spring,of constant 3.4 kN/m,rigidly attached to the plane.If the block's mass is 33.0 kg and it compresses the spring by 37.0 cm,find the distance the block travelled before it encountered the spring.

As a stone slides down a frictionless,ice-covered hill,its mechanical energy is conserved but its momentum is not conserved.

A tennis ball bounces on the floor three times.If each time it loses 22.0% of its energy due to heating,how high does it bounce after the third time,provided we released it 2.3 m from the floor?

You push a heavy box of mass m up a frictionless inclined plane of length l and height h in some time t₀.Later,you push the same box up a similar inclined plane of length l/2 and height h in the same time t₀.What can you say about the relationship between your power output(s)during these two processes? Assume the box is moved at a constant velocity in both cases.

A car drives 5.0 km north,then 7.3 km east,then 3.4 km northeast,all at a constant velocity.If the car had to perform 2.6 × 10⁶ J of work during this trip,what was the magnitude of the average frictional force on the car?

Joe and Bill throw identical balls vertically upward.Joe throws his ball with an initial speed of twice as high as Bill's ball.The maximum height of Joe's ball will be

When a moving object hits a stationary object and causes it to move,some of the moving object's kinetic energy is transformed into momentum in the object that was at rest.

A child pulls on a wagon with a force of 75 N.If the wagon moves a total of 42 m in 3 min,what is the average power generated by the child,in watts?

A prankster drops a water balloon from the top of a building on an unsuspecting person on the sidewalk below.If the balloon is traveling at 30.3 m/s when it strikes a person's head (1.5 m above the ground) ,how tall is the building? Neglect air resistance.

A massless spring hangs from the ceiling.How much does its potential energy increase,if a 28.8-kg mass is attached to it? The spring constant is 4800 N/m.

A child does work to climb to the top of a slide,thus giving herself potential energy.Explain what has happened to all this potential energy as the child,still moving,nears the bottom of the (not frictionless)slide.

You do 174 J of work while pulling your sister back on a swing,whose chain is 5.10 m long,until the swing makes an angle of 32.0° with the vertical.What is your sister's mass?

A helicopter descends vertically to land with a speed of 4.0 m/s.If the shock absorbers have an initial length of 0.50 m,they compress to 79% of their original length and the air in the tires absorbs 21% of the initial energy as heat,what is the ratio of the spring constant to the helicopter's mass? Assume one landing gear in the craft.

An airplane is observed to be 2.68 km from its takeoff point,at a horizontal distance of 2.66 km.What is the gravitational potential energy of the plane with respect to the ground? The plane's mass is 23.0 metric tons.