1. A weight lifter lifts a 330-N set of weights from ground level to a position over his head, a vertical distance
1. A weight lifter lifts a 330-N set of weights from ground level to a position over his head, a vertical distance
of 1.90 m. How much work does the weight lifter do, assuming he moves the weights at constant speed?
Answer: __________ J
2. A horizontal force of 150 N is used to push a 47.5-kg packing crate a distance of 6.40 m on a rough horizontal surface. If the crate moves at constant speed, find each of the following.
(a) the work done by the 150-N force
Answer: __________ J
(b) the coefficient of kinetic friction between the crate and the surface
Answer: ___________
3. A sledge loaded with bricks has a total mass of 18.5 kg and is pulled at constant speed by a rope inclined at 19.5° above the horizontal. The sledge moves a distance of 20.9 m on a horizontal surface. The coefficient of kinetic friction between the sledge and surface is 0.500.
(a) What is the tension in the rope?
Answer: __________ N
(b) How much work is done by the rope on the sledge?
Answer: ___________ kJ
(c) What is the mechanical energy lost due to friction?
Answer: ___________ kJ
4. A block of mass m = 2.50 kgis pushed d = 2.10 malong a frictionless horizontal table by a constant applied force of magnitude F = 12.0 N directed at an angle θ = 25.0°below the horizontal as shown in the figure below. Please see image corresponding to question on the attached document.
(a) Determine the work done by the applied force.
Answer: _________ J
(b) Determine the work done by the normal force exerted by the table.
Answer: _________ J
(c) Determine the work done by the force of gravity.
Answer: _________ J
(d) Determine the work done by the net force on the block.
Answer: _________ J
5. A mechanic pushes a 2.00 ✕ 103-kg car from rest to a speed of v, doing 5,370 J of work in the process. During this time, the car moves 21.0 m. Neglecting friction between car and road, find v and the horizontal force exerted on the car.
(a) the speed v
Answer: _________ m/s
(b) the horizontal force exerted on the car (Enter the magnitude.)
Answer: _________ N
6. Driving home from school one day you spot a ball rolling out into the street. You brake for 1.20 s, slowing your 980 kg car from 16.0 m/s to 9.50 m/s. Please see image corresponding to question on the attached document.
(a) What was the average force exerted on your car during braking?
Magnitude:
Answer: _______ kN
Direction:
Forward OR backward?
Answer: _______
(b) How far did you travel while braking?
Answer: _______ m
7. A 56.5-kg runner has a speed of 5.80 m/s at one instant during a long-distance event. (a) What is the runner’s kinetic energy at this instant?
Answer: _________ J
(b) If he doubles his speed to reach the finish line, by what factor does his kinetic energy change?
Kef/Kei=
Answer: _______
8. A 62-kg base runner begins his slide into second base when he is moving at a speed of 3.2 m/s. The coefficient of friction between his clothes and Earth is 0.70. He slides so that his speed is zero just as he reaches the base.
a) How much mechanical energy is lost due to friction acting on the runner?
Answer: ________ J
(b) How far does he slide?
Answer: _________ m
9. A running 54-kg cheetah has a top speed of 31 m/s.
(a) What is the cheetah’s maximum kinetic energy?
Answer: __________ J
(b) Find the cheetah’s speed when its kinetic energy is one half of the value found in part (a).
Answer: __________ m/s
10. A 7.80-g bullet moving at 470 m/s penetrates a tree trunk to a depth of 4.90 cm.
(a) Use work and energy considerations to find the average frictional force that stops the bullet.
Answer: _________ N
(b) Assuming the frictional force is constant, determine how much time elapses between the moment the bullet enters the tree and the moment it stops moving.
Answer: __________ s
11. A 0.35-kg particle has a speed of 3.0 m/s at point A and kinetic energy of 8.1 J at point B.
(a) What is its kinetic energy at A?
Answer: _________ J
(b) What is its speed at point B?
Answer: _________ m/s
(c) What is the total work done on the particle as it moves from A to B?
Answer: _________ J
12. A man pushing a crate of mass m = 92.0 kg at a speed of v = 0.855 m/s encounters a rough horizontal surface of length ℓ = 0.65 mas in the figure below. If the coefficient of kinetic friction between the crate and rough surface is 0.359 and he exerts a constant horizontal force of 290 N on the crate. Please see image corresponding to question on the attached document.
(a) Find the magnitude and direction of the net force on the crate while it is on the rough surface.
| magnitude | = ___________ N |
| direction | = ___________—Select—same as the motion of the crateopposite as the motion of the crate |
(b) Find the net work done on the crate while it is on the rough surface.
Answer: __________ J
(c) Find the speed of the crate when it reaches the end of the rough surface.
Answer: ___________ m/s
13. A daredevil on a motorcycle leaves the end of a ramp with a speed of 37.9 m/s as in the figure below. If his speed is 35.5 m/s when he reaches the peak of the path, what is the maximum height that he reaches? Ignore friction and air resistance. Please see image corresponding to question on the attached document.
Answer: ___________ m
14. A block of mass m = 5.90 kgis released from rest from point and slides on the frictionless track shown in the figure below. (Assume ha = 7.50 m.) Please see image corresponding to question on the attached document.
(a) Determine the block’s speed at points and B and C .
| point B | = ___________ m/s |
| point C | = ___________ m/s |
(b) Determine the net work done by the gravitational force on the block as it moves from point to point .
Answer: __________ J
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