Exam 8: Potential Energy and Conservation of Energy

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. )

What is the minimum energy needed to lift a 1.0-kg rocket to a height of 200 km and to give it a speed of 8.0 km/s at that height? (Neglect air resistance and the small decrease in g over that distance. )

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?

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.

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 v1=1.2 m/s. Upon separation from the spring,as shown in the figure.The block descends a ramp and has a velocity v2=1.5 m/ 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 v3=1.4 m/ 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 person stands on the edge of a cliff.She throws three identical rocks with the same speed.Rock X is thrown vertically upward,rock Y is thrown horizontally,and rock Z is thrown vertically downward.If the ground at the base of the cliff is level,which rock hits the ground with the greatest speed if there is no air resistance?

The figure shows a famous roller coaster ride.You can ignore friction.If the roller coaster leaves point Q from rest,what is its speed at the top of the 25-m peak (point S)?

If electricity costs 7.06¢/kW∙h,how much would it cost you to run a Stereo system Per day for

A heavy sled and a light sled,both moving horizontally with the same speed,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. )

A heavy dart and a light dart are launched horizontally on a frictionless table by identical ideal springs.Both springs were initially compressed by the same amount.Which of the following statements about these darts are correct? (There could be more than one correct choice. )

A heavy rock and a light rock are dropped from the same height and experience no significant air resistance as they fall.Which of the following statements about these rocks are correct? (There could be more than one correct choice. )

You and your friend,who weighs the same 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 you and your friend,after you both reach the top.

A 0.12-kg block is held in place against the spring by a 35-N horizontal external force.The external force is removed,and the block is projected with a velocity v₁=1.2 m/s. When it separates from the spring,as shown in the figure.The block descends a ramp and has a velocity v2=1.4 m/s. At the bottom of the ramp.The track is frictionless between points A and B.The block enters a rough section at B,extending to E.The coefficient of kinetic friction between the block and the rough surface is 0.26.The block moves on to D,where it stops.By how many centimeters was the spring initially compressed?

A 60-kg skier starts from rest from the top of a 50-m high slope.If the work done by friction is -6.0 kJ,what is the speed of the skier on reaching the bottom of the slope?

An ideal spring with a force constant (spring constant)of 15 N/m is initially compressed by 3.0 cm from its uncompressed position.How much work is required to compress the spring an additional 4.0 cm?

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)?

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 tension in the wire just as the ball swings through its lowest position?

An ideal spring with a spring constant (force constant)of Is stretched from equilibrium to 2.9 m.How much work is done in the process?

You do 116 J of work while pulling your sister back on a frictionless swing,whose chain is Long,until the swing makes an angle of 32.0° with the vertical.What is your sister's mass?

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