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Transcript
From College Physics by Serway & Faughn
American Community School
Gr.10 HS Physics
Newton Laws of Motion
Conceptual Questions:
1. If a car is traveling westward with a constant speed of 20 m/s, what is the resultant
force acting on it?
2. If a car moves with a constant acceleration, can you conclude there are no forces acting
on it?
3. A rubber ball is dropped onto the floor. What force causes the ball to bounce?
4. A passenger sitting in the rear of a bus claims that she was injured as the driver
slammed on the brakes, causing a suitcase to come flying toward her from the front of
the bus. If you were the judge in this case, what disposition would you make? Why?
5. In the motion picture It Happened One Night (Columbia Pictures, 1934), Clark Gable
is standing inside a stationary bus in front of Claudette Colbert, who is seated. The bus
suddenly starts moving forward and Clark falls into Claudette's lap. Why did this
happen?
6. If gold were sold by weight, would you rather buy it in Denver or in Death Valley? If it
were sold by mass, in which of the two locations would you prefer to buy it? Why?
7. A space explorer is moving through space far from any planet or star. She notices a
large rock, taken as a specimen from an alien planet, floating around the cabin of the
ship. Should she push it gently or kick it toward the storage compartment? Why?
8. As a rocket is fired from a launching pad, its speed and acceleration increase with time
as its engines continue to operate. Explain why this occurs even though the thrust of
the engines remains constant.
9. A truck loaded with sand accelerates along a highway. If the driving force on the truck
remains constant, what happens to the truck's acceleration if its trailer leaks sand at a
constant rate through a hole in its bottom?
10. A ball is held in a person's hand. (a) Identify all the external forces acting on the ball
and the reaction to each. , (b) If the ball is dropped, what force is exerted on it while it
is falling? Identify the reaction force in this case. (Neglect air resistance.)
11. What force causes an automobile to move? A propellerdriven airplane? A rowboat?
From College Physics by Serway & Faughn
12. In a tug-of-war between two athletes, each pulls on the rope with a force of 200 N.
What is the tension in the rope? If the rope does not move, what horizontal force does
each athlete exert against the ground?
13. Identify the action-reaction pairs in the following situations: (a) A man takes a step,
(b) a snowball hits a girl in the back, (c) a baseball player catches a ball, (d) a gust of
wind strikes a window.
Problems:
1. A 6.0-kg object undergoes an acceleration of 2.0 m/s2. (a) What is the magnitude of the
resultant force acting on it? (b) If this same force is applied to a 4.0-kg object, what
acceleration is produced?
2. A football punter accelerates a football from rest to a speed of 10 m/s during the time
in which his toe is in contact with the ball (about 0.20 s). If the football has a mass of
0.50 kg, what average force does the punter exert on the ball?
3. A freight train has a mass of 1.5 x 107 kg. If the locomotive can exert a constant pull of
7.5 x 105 N, how long does it take to increase the speed of the train from rest to 80
km/h?
4. The air exerts a forward force of 10 N on the propeller of a 0.20-kg model airplane. If
the plane accelerates forward at 2.0 m/s2, what is the magnitude of the resistive force
exerted by the air on the airplane?
5. A 5.0-g bullet leaves the muzzle of a rifle with a speed of 320 m/s. What total force
(assumed constant) is exerted on the bullet while it is traveling down the 0.82-m-long
barrel of the rifle?
6. A performer in a circus is fired from a cannon as a “human cannonball” and leaves the
cannon with a speed of 18.0 m/s. The performer’s mass is 80.0 kg. The cannon barrel
is 9.20 m long. Find the average the net force exerted on the performer while he is
being accelerated inside the cannon.
7. To lift a patient, four nurses grip the sheet on which the patient is lying and lift
upward. If each nurse exerts an upward force of 240 N and the patient has an upward
acceleration of 0.504 m/s2, what is the weight of the patient?
8. A boat moves through the water with two forces acting on it. One is a 2000-N forward
push by the water on the propeller, and the other is an 1800-N resistive force due to
the water around the bow. (a) What is the acceleration of the 1000-kg boat? (b) If it
starts from rest, how far will it move in 10.0 s? (c) What will its velocity be at the end
of this time?
From College Physics by Serway & Faughn
9. Two forces are applied to a car in an effort to move it, as shown in the figure below.
(a) What is the resultant of these two forces? (b) If the car has a mass of 3000 kg, what
acceleration does it have? Ignore friction.
10. The force exerted by the wind on the sails of a sailboat
is 390 N north. The water exerts a force of 180 N east.
If the boat (including crew) has a mass of 270 kg, what
are the magnitude and direction of its acceleration?