Exam 6: Work and Energy

Use the figure to answer the question. A light rope runs through two frictionless pulleys of negligible mass.A mass,m,is hung from one of the pulleys and a force,F is applied to one end of the rope so that the mass moves at a constant speed. -What is the force needed to move the mass at a constant speed?

A 5-kg object undergoes a displacement $\Delta$ = 2 + 3 .During the displacement,a constant force = 4 - 2 acts on the object.All values are given in SI units.The work done by the force on this object is

A body is acted upon by a force of 10 N and undergoes displacement in the direction of the force in accordance with the relation where the units are SI.The rate at which the force is doing work at the instant t = 2 s is

If vector = -2 + 3 and a vector = 4 - 5 ,the inner product · is

A donkey is attached by a rope to a wooden cart at an angle of 23 ^$\circ$ to the horizontal.The tension in the rope is 210 N.If the cart is dragged horizontally along the floor with a constant speed of 6 km/h,calculate how much work the donkey does in 35 minutes.

A particle that is subjected to a variable force travels a distance of 20 m in a straight line in the same direction as the force.The force varies as follows: What was the total work done by this force during the full 20-m trip?

A skier of mass 50 kg is moving at speed 10 m/s at point P₁ down a ski slope with negligible friction.What is the skier's kinetic energy when she is at point P₂,20 m below P₁?

The human heart is essentially a pump for moving blood around the body.If its average power output (over many beats)is about 2.0 W and it pumps blood at an overall average speed of 0.3 m/s into the output aorta channel,calculate the average force with which the heart moves the blood into the aorta.

A variable force is represented on an F-versus-x graph.Which of the following is the work done by this force?

Consider two engines.The larger is rated at 2 W and the smaller at 1 W.The smaller one can do a certain quantity of work in 2 h.The larger can do twice as much work in a time of

The weight of an object on the moon is one-sixth its weight on Earth.A body moving with a given speed on the moon has kinetic energy equal to ______________ it would have if it were moving at the same speed on Earth.

Two forces,both of magnitude 12 N and directed 35 degrees either side of the direction of motion,pull a crate 15 m.How much work is done by the forces in moving the crate?

What is the work done by a car's braking system when it slows the 1500-kg car from an initial speed of 96 km/h down to 56 km/h in a distance of 55 m?

Car drag racing takes place over a distance of a mile (402 m)from a standing start.If a car (mass 1500 kg)could be propelled forward with a pulling force equal to that of gravity,what would be the change in kinetic energy and the terminal speed of the car (in mph)at the end of the race be? (For comparison,a modern,high-performance sports car may reach a terminal speed of just over 100 mph = 44.7 m/s.)

Use the figure for the question. The graph shows the speed of a light truck of mass 4000 kg coasting on neutral down a level straight road.The truck is slowing down due to air resistance and rolling friction. -The net force at 25s is ____ the net force at 5s.

A Blackhawk helicopter is winching up an injured soldier from a danger zone.The soldier and his kit have a mass of 150 kg and are pulled up 50 m in the air at a steady rate.If it takes 30 s to pull the soldier up,how much power has been used by the helicopter's 65% efficient winch engine?

A 50% efficient hydroelectric power plant generates electricity from water falling a height of 110 m and at a rate of x kg/s.If the maximum possible power output of the plant was 27.0 MW,what is x?

The average marathon runner can complete the 42.2-km distance of the marathon in 3 h and 30 min.If the runner's mass is 75 kg,what is the runner's average kinetic energy during the run?

A vertical light spring stretches a distance h meters when a mass m is hung from it.The spring/mass system is now placed on a horizontal frictionless table and set into oscillation with amplitude h and maximum velocity v.What is the total energy involved in the spring/mass oscillating system.

Egyptian pyramid workers push a 1200-kg block up an incline that has an angle of 69 degrees to the vertical,at a constant speed of 0.5 m/s.The coefficient of kinetic friction between the block and the incline surface is 0.44.How much power must the workers supply?