Exam 7: Work and Energy

Three cars (car F,car G,and car H)are moving with the same speed and slam on their brakes.The most massive car is car F,and the least massive is car H.If the tires of all three cars have identical coefficients of kinetic friction with the road surface,which car travels the longest distance to skid to a stop?

A bead is moving with a speed of 20 m/s at position A on the track shown in the figure.This track is friction-free,and there is no appreciable air resistance.What is the speed of the bead at point C?

A 1500-kg car accelerates from rest to 25 m/s in 7.0 s.What is the average power delivered by the engine? (1 hp = 746 W)

A heavy dart and a light dart are launched vertically by identical ideal springs.Both springs were initially compressed by the same amount.There is no significant air resistance.Which of the following statements about these darts are correct? (There could be more than one correct choice.)

A proton of mass m is at rest when it is suddenly struck head-on by an alpha particle (which consists of 2 protons and 2 neutrons)moving at speed v.If the collision is perfectly elastic,what speed will the alpha particle have after the collision? (Assume the neutron's mass is equal to the proton's mass.)

How many joules of energy are used by a 2.0 hp motor that runs for 1.0 hour? (1 hp = 746 W)

A person carries a 25.0-N rock (the system)through the path shown in the figure,starting at point A and ending at point B.The total time from A to B is 1.50 min.How much work did the gravitational force exerted on the rock by Earth do on the rock between A and B?

A person carries a 2.00-N pebble through the path shown in the figure,starting at point A and ending at point B.The total time from A to B is 6.75 min.How much work did the gravitational force exerted on the pebble by Earth do on the pebble between A and B?

On an alien planet,an object moving at 4.0 m/s on the horizontal ground comes to rest after traveling a distance of 10 m.If the coefficient of kinetic friction between the object and the surface is 0.20,what is the value of g on that planet?

An 825-kg space vehicle is circling Earth in a circular orbit with a radius of 10,300 km.Its orbit is to be changed to a larger circle with a radius of 17,400 km.How much energy is required to accomplish this? The mass of Earth is 5.97 × 10²⁴ kg and G = 6.67 × 10^-11 N ∙ m²/kg^2.

A 0.46-kg block is held in place against the spring by a 30-N horizontal external force.The external force is removed,and the block is projected with a velocity $v 1 = 1.2 \mathrm {~m} / \mathrm { s }$ upon separation from the spring,as shown in the figure.The block descends a ramp and has a velocity $v _ { 2 } = 1.5 \mathrm {~m} / \mathrm { s }$ at the bottom.The track is frictionless between points A and B.The block enters a rough section at point B,extending to E.The coefficient of kinetic friction between the block and the rough surface is 0.38.The velocity of the block is $v _ { 3 } = 1.4 \mathrm {~m} / \mathrm { s }$ at point C.The block moves on to D,where it stops.What distance does the block travel between points B and D?

A 1000-kg car is moving at 15 km/h.If a 2000-kg truck has 23 times the kinetic energy of the car,how fast is the truck moving?

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 effects.

Water flows over a waterfall that is 20 m high at the rate of 4.0 × 10⁴ kg/s.If this water powers an electric generator with a 40% efficiency,how many watts of electric power can be supplied?

When a car of mass $1167 \mathrm {~kg}$ accelerates from 10.0 m/s to some final speed,4.00 × 10⁵ J of work are done on it by the frictional force exerted on the car by the road's surface.Find this final speed.

An egg falls from a bird's nest in a tree and feels no effects due to the air.As it falls,

A 30-N box is pulled upward 6.0 m along the surface of a ramp that rises at 37° above the horizontal.How much work does the gravitational force exerted on the box by Earth do on the box during this process?

A sled is moving along a horizontal surface with a speed of 5.7 m/s.It then slides up a rough hill having a slope of 11° above the horizontal.The coefficient of kinetic friction between the sled and the surface of the hill is 0.26.How far along the surface does the block travel up the incline?

A child pulls on a wagon with a force of $75 \mathrm {~N}$ If the wagon moves a total of $42 \mathrm {~m}$ in $3.1 \mathrm {~min}$ what is the average power delivered by the child?

A heavy sled and a light sled,both moving horizontally with the same kinetic energy,suddenly slide onto a rough patch of snow and eventually come to a stop.The coefficient of kinetic friction between the sleds and the rough snow is the same for both of them.Which of the following statements about these sleds are correct? (There could be more than one correct choice.)