PHYSICS LEVEL 2
Name _______________________________________________________
Period _______________
NEWTON’S LAWS TINKHAM QUESTIONS
1. A stone is thrown from the top of a cliff. As the stone falls, is it in equilibrium? Explain, ignoring air
resistance.
2. Describe friction. What is the difference between kinetic and static friction?
3. What is the function of the normal force?
4. Can an object ever be in equilibrium if the object is acted on by only
a. a single nonzero force?
b. two forces that point perpendicular to each other?
c. two forces that point in directions that are not perpendicular?
5. A person has a choice of either pushing or
pulling a sled at a constant velocity, as the
drawing illustrates. Friction is present. If the
angle  is the same in both cases, does it
require less force to push or to pull? Explain.
6. A skier is standing motionless on a horizontal patch of snow. She is holding onto a horizontal tow
rope, which is about to pull her forward. The skier’s mass is 59 kg, and the coefficient of static friction
between the skis and the snow is 0.14. What is the maximum force that the tow rope can apply to skier
without causing her to move? Include a free body diagram and a force chart.
7. A 950 N clock initially at rest on a horizontal floor requires a 650 N horizontal force to set it in
motion. After the clock is in motion, a horizontal force of 560 N keeps it moving with a constant
velocity.
a. What is the coefficient of static friction (s)?
b. What is the coefficient of kinetic friction (k)?
8. A mountain climber, in the process of crossing between two cliffs by a rope, pauses to rest. As the
drawing shows, she is closer to the left cliff than to the right cliff, with the result that the tensions in the
left and right sides of the rope are not the same. The tension in the right rope is 845.3 N. Find the
tension in the left rope and the mass of the climber. Include a free body diagram and a force chart.
9. A Mercedes-Benz 300SL (m = 1700 kg) is parked on a road that rises 15 above the horizontal.
Calculate the normal force and the coefficient of static friction. Include a free body diagram and a force
chart.
10. A 60 kg crate rests on a level floor at a shipping dock. The coefficients of static and kinetic friction
0.760 and 0.410, respectively. What horizontal force is required to just start the crate moving and slide
the crate across the dock at a constant speed?
11. Why do you lunge forward when your car suddenly comes to a halt? Why are you pressed backward
against the seat when your car rapidly accelerates?
12. A bird feeder of large mass is hung from a tree limb, as the drawing
shows. A cord attached to the bottom of the feeder has been left dangling
free. Curiosity gets the best of a child, who pulls on the dangling cord in an
attempt to see what’s in the feeder. The dangling cord is cut from the same
source as the cord attached to the limb. Is the cord between the feeder and
the limb more likely to snap with a slow continuous pull or a sudden
downward pull? Explain.
13. The net external force acting on an object is zero. Is it possible for the object to be traveling with a
velocity that is not zero? If your answer is yes, state whether any conditions must be placed on the
magnitude and direction of the velocity. If your answer is no, provide a reason for your answer.
14. Is a net force being applied to an object when the object is moving downward with a constant
acceleration of 9.80 m/s2? Explain.
15. Is a net force being applied to an object when the object is moving downward with a constant
velocity of 9.80 m/s? Explain.
16. Newton’s second law indicates that when a net force acts on an object, it must accelerate. Does this
mean that when two or more forces are applied to an object simultaneously, it must accelerate? Explain.
17. During the final stages of descent, a sky diver with an open parachute approaches the ground with a
constant velocity. The wind does not blow him from side to side. Is the sky diver in equilibrium and, if
so, what forces are responsible for the equilibrium?
18. The force of air resistance acts to oppose the motion of an object moving through the air. A ball is
thrown upward and eventually returns to the ground.
a. As the ball moves upward, is the net force that acts on the ball greater than, less than, or equal
to its weight? Explain.
b. Repeat part (a) for the downward motion of the ball.
19. Two people are pushing a stalled car, as the figure below indicates. The mass of the car is 1850 kg.
One person applies a force of 275 N, while the other applies a force of 395 N. The force of friction is
560 N. Find the acceleration of the car.
20. A man is stranded on a raft (mass of man and raft = 1300 kg). By paddling, he causes an average
force of 17 N applied to the raft in a direction due east. The wind also exerts a force on the raft of 15 N
and points west.
a. Ignoring any friction from the water, find the raft’s acceleration.
b. The initial velocity of the raft is 0.15 m/s due east. If the forces are maintained for 65 s, find
the raft’s displacement during this time interval.
21. A sled and its rider with a mass of 35 kg are moving at a speed of 4 m/s along a horizontal stretch of
snow. The snow exerts a kinetic frictional force on the runners of the sled, so the sled slows down and
eventually comes to a stop. The coefficient of kinetic friction is 0.05. What is the acceleration of the
sled? Include a free body diagram and a force chart.
22. An automobile engine is being positioned above an engine compartment, as seen in the figure. To
position the engine, a worker is using a rope, which he pulls on with a force T2 = 582 N at 10 below the
+x-axis. Find the tension T1 in the supporting cable, which is angled at 80 above the –x-axis, and the
mass of the engine. Include a force chart.
23. During a circus performance, a 72 kg human cannonball is shot out of an 18 m long cannon. If the
human cannonball spends 0.95 s in the cannon, determine the net force exerted on him in the barrel of
the cannon.
24. A 15 g bullet is fired from a rifle. It takes 2.5 x 10-3 s for the bullet to travel the length of the barrels,
and it exit the barrel with a speed of 715 m/s. Find the net force exerted on the bullet.
25. Newton’s second law is written as F = ma; however, it describes the effects of force and mass on
acceleration.
a. Rearrange the equation to solve for a (a = …).
b. Describe the relationship between force and acceleration.
c. Describe the relationship between mass and acceleration.
26. A fisherman is fishing from a bridge and is using a “45 N test line.” In other words, the line will
sustain a maximum force of 45 N without breaking. What is the weight of the heaviest fish that can be
pulled up vertically when the line in reeled in
a. What is the weight of the heaviest fish that can be pulled up vertically when the line in reeled
in at a constant speed?
b. What is the mass of the heaviest fish that can be pulled up vertically when the line in reeled in
with an acceleration of 2 m/s2? Include a free body diagram.
27. A 35 kg crate is sliding down a ramp that is inclined at an angle of 30 above the horizontal. The
coefficient of kinetic friction between the crate and the ramp surface is 0.6. Find the acceleration of the
moving crate. Include a free body diagram and a force chart.
28. A 17 kg toboggan slides down a hill and has a constant velocity. The angle of the hill is 8 with
respect to the horizontal. What is the coefficient of kinetic friction between the surface of the hill and
the toboggan? Include a free body diagram and a force chart.
29. A 52 kg student is skateboarding down a ramp that is 6 m long and inclined at 18 with respect to the
horizontal. The initial speed of the skateboarder at the top of the ramp is 2.6 m/s. Neglect friction.
a. What is the acceleration of the skateboarder? Include a free body diagram and a force chart.
b. What is the speed of the skateboarder at the end of the ramp?
30. According to Newton’s third law, when you push on an object, the object pushes back on you with
an oppositely directed force of equal magnitude. If the object is a massive crate resting on the floor, it
will probably not move. Some people think that the reason the crate does not move is that the two
oppositely directed pushing forces cancel. Explain why this logic is faulty and why the crate does not
move.
31. A rope is used in a tug-of-war between two teams of five people each. Both teams are equally
strong, so neither team wins. An identical rope is tied to a tree, and the same ten people pull just as hard
on the loose end as they did in the contest. In both cases, the people pull steadily with no jerking.
Which rope, if either, is more likely to break? Explain.
32. A circus performer hangs stationary from a rope. She then begins to climb upward by pulling herself
up, hand over hand. When she starts climbing, is the tension in the rope less than, equal to, or greater
than it is when she hangs stationary? Explain.
33. A weight hangs from a ring at the middle of a rope, as the drawing illustrates. Can the person who is
pulling on the right end of the rope ever make the rope perfectly horizontal? Explain your answer in
terms of the forces that act on the ring.
34. A father and his seven-year-old daughter are facing each other on ice skates. With their hands, they
push off against one another.
a. Compare the magnitudes of the pushing forces that they experience. Explain.
b. Which one, if either, experiences the larger acceleration? Explain.
35. A gymnast is bouncing on a trampoline. After a high bounce the gymnast comes down and hits the
elastic surface of the trampoline. In so doing the gymnast applies a force to the trampoline.
a. Describe the effect this force has on the elastic surface.
b. The surface applies a reaction force to the gymnast. Describe the effect that this reaction force
has on the gymnast.
36. What force does the scale read in the figure below? Explain.
37. Arnold Strongman and Suzie Small pull on opposite ends of a rope in a tug of war. Who exerts the
greatest force on the rope? Explain.
38. Two people of equal mass, 6 meters apart, attempt a tug of war on frictionless ice. If they pull on
opposite ends of the rope with equal force, each slides 3 meters to a point midway between them.
Suppose instead that only one person pulls and the other fastens the rope around his or her waist. How
far does each person slide? (Neglect any effects of the rope’s mass.)
39. Consider the apple at rest on the table. If we call the gravitational force exerted on the apple action,
what is the reaction force according to Newton’s 3rd Law?
40. The mass of a spacecraft is 11,000 kg and the mass of an astronaut is 92 kg. The astronaut exerts a
push P = +36 N on the spacecraft. Find the acceleration of the spacecraft and the acceleration of the
astronaut.