Exam 7: Work and Energy

A 35-N bucket of water is lifted vertically 3.0 m and then returned to its original position.How much work did the gravitational force exerted by Earth on the object do on the bucket during this process?

The mass of Earth is 9.31 times the mass of Mars,and the radius of Earth is 1.88 times the radius of Mars.The escape speed for Mars is what percent of the escape speed for Earth?

It takes 87 J of work to stretch an ideal spring from 1.4 m to 2.9 m from equilibrium.What is the value of the spring constant of this spring?

A roller coaster starts from rest at a height h at the left side of a loop-the-loop,as shown in the figure.It is not attached to the track in anyway,and there is no friction from the track or from air resistance.If the radius of the loop is R = 6.0 m,what is the minimum height h for which the roller coaster will not fall off the track at the top of the loop?

A crane lifts a 425 kg steel beam vertically upward a distance of $95 \mathrm {~m} .$ How much work does the crane do on the beam if the beam accelerates upward at 1.8 m/s²? Neglect frictional forces.

In a ballistics test,a 28-g bullet pierces a sand bag that is $30 \mathrm {~cm}$ thick.If the initial bullet velocity was $55 \mathrm {~m} / \mathrm { s }$ and it emerged from the sandbag moving at $18 \mathrm {~m} / \mathrm { s } \text {, }$ what was the magnitude of the friction force (assuming it to be constant)that the bullet experienced while it traveled through the bag?

You and your friend,who has the same mass as you,want to go to the top of the Eiffel Tower.Your friend takes the elevator straight up.You decide to walk up the spiral stairway,taking longer to do so.Compare the gravitational potential energy of the system you-Earth and your friend-Earth,after you both reach the top.

A block of mass m = 4.4 kg,moving on frictionless surface with a speed $v _ { \mathrm { i } } = 9.2 \mathrm {~m} / \mathrm { s }$ makes a sudden perfectly elastic collision with a second block of mass M,as shown in the figure.The second block is originally at rest.Just after the collision,the 4.4-kg block recoils with a speed of $v _ { \mathrm { f } } = 2.5 \mathrm {~m} / \mathrm { s }$ What is the mass M of the second block?

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 m? Friction in the system is negligible.

A stone can slide down one of four different frictionless ramps,as shown in the figure.For which ramp will the speed of the ball be the greatest at the bottom?

A 5.0-N projectile leaves the ground with a kinetic energy of 220 J.At the highest point in its trajectory,its kinetic energy is 120 J.To what vertical height,relative to its launch point,did it rise if there was no air resistance?

How many joules of energy are used by a 1.0-hp motor that runs for 1.0 hour? (1 hp = 746 W)

On a planet where g = 10.0 m/s² and air resistance is negligible,a sled is at rest on a rough inclined hill rising at 30° as shown in the figure.The sled is allowed to move and it stops on a rough horizontal surface,at a distance of 4.0 m from the bottom of the hill.The coefficient of kinetic friction on the hill is 0.40.What is the coefficient of kinetic friction between the horizontal surface and the sled?

The value of g at the surface of the spherical Asteroid X is 0.0060 m/s² and the escape velocity is 10.1 m/s.What is the mass of this asteroid? (G = 6.67 × 10^-11 N ∙ m²/kg²)

Assuming negligible friction,what spring constant would be needed by the spring in a "B-B gun" to fire a 10-g pellet to a height of 100 m if the spring is initially compressed by 0.10 m?

A firecracker explodes in midair and breaks up into many fragments.Which of the following statements are true regarding conditions immediately before and immediately after the explosion: I.The total momentum of the fragments is equal to the original momentum of the firecracker. II.The total kinetic energy of the fragments is equal to the original kinetic energy of the firecracker.

Two objects of different mass have equal,non-zero kinetic energies.Which object has the greater magnitude momentum?

How much work is required to stretch an ideal spring of spring constant 40 N/m from x = 0.20 m to x = 0.25 m if the unstretched position is at x = 0.00 m?

A 2.0-kg object (the system)is lifted vertically through 3.00 m by a constant 150-N force.How much work did Earth do on the object during this process?

A stone is moving on a rough level surface.It has 24 J of kinetic energy,and the friction force exerted on it by the surface is a constant 0.50 N.What is the maximum distance it can slide?