Exam 7: Work and Energy

A child does 350 J of work while pulling a box from the ground up to his tree house at a steady speed with a light rope.The tree house is $4.0 \mathrm {~m}$ above the ground.What is the mass of the box?

A certain spherical asteroid has a mass of is 4.65 × 10¹⁷ kg and a radius of 39,600 m.If a 150-kg object is dropped from rest at an altitude of 12,400 m above the surface of this asteroid,with what speed will it hit the surface? (G = 6.67 × 10^-11 N ∙ m²/kg²)

Two objects,one of mass m and the other of mass 2m,are dropped from the top of a building.Assuming there is no air resistance,when they hit the ground

An ideal spring stretches by 21.0 cm when a 135-N object is hung from it.If instead you hang a fish from this spring,what is the weight of a fish that would stretch the spring by $31.0 \mathrm {~cm} ?$

How fast must a 6.0-kg cat run to have a kinetic energy of 150 J?

A truck has four times the mass of a car and is moving with twice the speed of the car.If K_t and K_c refer to the kinetic energies of truck and car respectively,it is correct to say that

You want to store 1,000 J of energy in an ideal spring when it is compressed by only 2.5 cm.What should be the spring constant of this spring?

A rock falls from a vertical cliff that is 4.0 m tall.At what speed will the gravitational potential energy of the rock-Earth system (relative to the base of the cliff)be equal to its kinetic energy? Assume that air has no effect on the motion of the rock.

A 1321-kg car climbs a 5.0° slope at a constant speed of $80.0 \mathrm {~km} / \mathrm { h }$ Assuming that air resistance may be neglected,at what rate (in kW)must the engine deliver energy to the drive wheels of the car?

A frictionless simple pendulum,with a small but dense 4.4-kg bob 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 bob swing on the other side? (b)What is the speed of the bob at the bottom of the swing?

Three cars (car L,car M,and car N)are moving with the same speed and slam on their brakes.The most massive car is car L,and the least massive is car N.If the tires of all three cars have identical coefficients of kinetic friction with the road surface,for which car is the amount of work done by friction in stopping it the greatest?

An object with a mass of 10 kg is initially at rest at the top of a frictionless inclined plane that rises at 30° above the horizontal.At the top,the object is initially 8.0 m from the bottom of the incline,as shown in the figure.When the object is released from this position,it eventually stops at a distance d from the bottom of the inclined plane along a horizontal surface,as shown.The coefficient of kinetic friction between the horizontal surface and the object is 0.20,and air resistance is negligible.Find the distance d.

An ideal spring with a spring constant of $22 \mathrm {~N} / \mathrm { m }$ is stretched from equilibrium to 2.9 m.How much work is done in the process?

A 1-kg ball is released from a height of 6 m,and a 2-kg ball is released from a height of 3 m.Air resistance is negligible as they fall.Which of the following statements about these balls are correct? (There could be more than one correct choice.)

How large a net force is required to accelerate a 1600-kg SUV from rest to a speed of 25 m/s in a distance of 200 m?

A 320-g air track cart traveling at 1.25 m/s suddenly collides elastically with a stationary 270-g cart.What is the speed of the 270-g cart just after the collision?

In a museum exhibit of a simple pendulum,a very small but dense 6.0-kg ball swings from a very light 2.5-m wire.The ball is released from rest when the pendulum wire makes a 65° angle with the vertical,and it swings in a circular arc with no appreciable friction or air resistance.What is the force that the wire exerts on the ball just as the ball swings through its lowest position?

Swimmers at a water park have a choice of two frictionless water slides,as shown in the figure.Although both slides drop over the same height h,slide 1 is straight while slide 2 is curved,dropping quickly at first and then leveling out.How does the speed v₁ of a swimmer reaching the bottom of slide 1 compare with v₂,the speed of a swimmer reaching the end of slide 2?

How do the escape speeds for two rockets,the first weighing 20 N and the second weighing 20,000 N compare?

A rubber ball bounces off of a wall with an initial speed v and reverses its direction so its speed is v right after the bounce.As a result of this bounce,which of the following quantities of the ball are conserved? (There could be more than one correct choice.)