Download Conservation of ME, Work, and Net Work/Change in KE

Conservation of ME, Work, and Net Work/Change in KE
1-26) Suppose the water at the top of Niagara Falls has a horizontal speed of 2.7 m/s just before it
cascades over the edge of the falls. If the height of the falls is 59 m, what is the magnitude of the
water’s velocity just before the water strikes the bottom? (Assume the water is in free fall once it passes
over the top of the falls.)
2-35) A golfer standing on the fairway hits a shot to a green that is elevated 6 m above the fairway. If
the ball leaves the golf club going 43 m/s at an angle of 40 degrees above horizontal, find the impact
speed of the ball.
3-4) When spring arrives Andy packs his winter clothes in a box and lifts it at a constant velocity to the
top shelf of his closet, a distance of 1.8 m above the floor. The clothes weigh 150 N. How much work
does Andy do in lifting the clothes?
4-6) You are moving into your dorm room at the beginning of the semester. Your weight is 685 N and
that of your belongings is 915 N.
A) How much work does the elevator do in lifting you and your belongings up five stories (15.2
m) with a constant velocity?
B) How much work does the elevator do on you (without belongings) on the downward trip
which is also made at a constant velocity?
5-8) Find the work done (by the force of gravity) on a bicyclist and his bike (m = 86 kg) as he coasts 180
m down a hill declined at 21 degrees below horizontal. Then find the work done by gravity on the
bicyclist as the bicyclist pedals up the same hill for 75 m.
6-13) A water skier whose mass is 70.3 kg has an initial speed of 6.1 m/s. Later, the speed of the skier is
11.3 m/s. Determine the work done by the net force acting on the skier.
7-14) A 0.075 kg arrow is fired horizontally. The bowstring exerts an average force of 65 N on the
arrow over a distance of 0.9 m. With what speed does the arrow leave the bow?
8-15) A 65 kg jogger is running at a speed of 5.3 m/s.
A) What is the kinetic energy of the jogger?
B) How much work is done by the net force that accelerated the jogger from rest?
9-16) A pitcher hurls a 0.25 kg softball. The softball starts from rest and leaves the throwers hand at a
speed of 25 m/s. How much work is done on the softball by the pitcher’s arm?
10-18) A 1200 kg car coasts through a 50 m long snow drift that is across the road (I swear I had nothing
to do with it). The car hits the snow going 20 m/s and emerges from the snow going only 8 m/s. Find
the average net force acting on the car as it coasts through the drift including the direction of this net
force relative to the displacement.
11-19) A 50000 kg space probe is traveling at a speed of 11000 m/s through deep space. Retrorockets
are fired along the line of motion that reduces the speed of the probe. The retrorockets generate a force
of 400000 N over a distance of 2500 km. What is the final speed of the probe?