Download Chapter 3: Newton`s Laws of Motion End of Chapter Questions

Chapter 3: Newton’s Laws of Motion
End of Chapter Questions
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What did Galileo discover in his legendary experiment on the Leaning Tower?
What does it mean to say a moving object has inertia? Give an example.
Is inertia the reason for moving objects maintaining motion, or the name given to this property?
What is the net force on a cart that is pulled to the right with 100 pounds and to the left with 30
pounds?
5. Why do we say that force is a vector quantity?
6. What does it mean to say something is in mechanical equilibrium?
7. Consider a book that weighs 15 N at rest on a flat table. How many newtons of support force
does the table provide? What is the net force on the book in this case?
8. When you stand at rest on a bathroom scale, how does your weight compare with the support
force by the scale?
9. A bowling ball at rest is in equilibrium. Is the ball in equilibrium when it moves at constant speed
in a straight-line path?
10. If you push on a crate with a force of 100 N and it slides at constant velocity, how much is the
friction acting on the crate?
11. What relationship does mass have with inertia?
12. What relationship does mass have with weight?
13. Which is more fundamental, mass or weight? Which varies with location?
14. Fill in the blanks: Shake something to and fro and you're measuring its _______. Lift it against
gravity and you're measuring its _______.
15. Fill in the blanks: The Standard International unit for mass is the _______. The Standard
International unit for force is the _______.
16. What is the weight of a 1-kilogram brick?
17. If the net force acting on a sliding block is somehow tripled, by how much does the acceleration
increase?
18. If the mass of a sliding block is tripled while a constant net force is applied, by how much does
the acceleration decrease?
19. If the mass of a sliding block is somehow tripled at the same time the net force on it is tripled,
how does the resulting acceleration compare to the original acceleration?
20. How does the direction of acceleration compare with the direction of the net force that produces
it?
21. Why doesn't a heavy object accelerate more than a light object when both are freely falling?
22. What is the net force that acts on a 10-N falling object when it encounters 4 N of air resistance?
10 N of air resistance?
23. What two principal factors affect the force of air resistance on a falling object?
24. What is the acceleration of a falling object that has reached its terminal velocity?
25. Why does a heavy parachutist fall faster than a lighter parachutist who wears the same size
parachute?
26. If two objects the same size fall through air at different speeds, which encounters the greater air
resistance?
27. How many forces are required for an interaction?
28. The Earth pulls down on you with a gravitational force that you call your weight. Do you pull up
on the Earth with the same amount of force?
29. If the forces that act on a bullet and the recoiling gun from which it is fired are equal in
magnitude, why do the bullet and gun have very different accelerations?
30. What is the acceleration of a 40-kg block of cement when pulled sideways with a net force of
200 N?
31. If a mass of 1kg is accelerated 1 m/s2 by a force of 1 N, what would be the acceleration of 2 kg
acted on by a force of 2 N?
32. How much acceleration does a 747 jumbo jet of mass 30,000 kg experience in takeoff when the
thrust for each of the four engines is 30,000 N?
33. A firefighter of mass 80 kg slides down a vertical pole with an acceleration of 4 m/s2. What is
the friction force that acts on the firefighter?
34. What will be the acceleration of a skydiver when air resistance builds up to be equal to half her
weight?
35. A boxer punches a sheet of paper in mid air, and brings it from rest to a speed of 25 m/s in
0.05 s. If the mass of the paper is 0.003 kg, what force does the boxer exert on it?
36. If you stand next to a wall on a frictionless skateboard and push the wall with a force of 30 N,
how hard does the wall push on you? If your mass is 60 kg, what’s your acceleration?
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He discovered that heavy and light objects fall at about the same speeds.
To say a moving object has inertia is to say it has the property of tending to keep moving ahead. Toss a bowling ball onto a bowling
alley and it keeps moving of itself–that is, of its own inertia.
Inertia is the name given to the property of objects to maintain their state of motion. (We don’t know the reason.)
The net force is 70 pounds to the right.
Force is a quantity that has both magnitude and direction.
Something in mechanical equilibrium is something wherein all the forces acting on it have a net force of zero.
The support force is 15 N. Since both forces are equal in magnitude and opposite in direction, the net force on the book is zero.
They have equal magnitudes. The support force shows your weight.
Yes.
Also 100 N, in the opposite direction, making the net force zero.
Mass is a measure of inertia. The greater the mass, the greater the resistance to changes in motion.
Weight and mass are directly proportional to each other. A change in one is the same kind of change in the other.
Mass is more fundamental, for all material objects have mass. Weight, however, depends on location.
Mass; weight.
Kilogram; newton.
About 10 newtons (more precisely, 9.8 newtons).
Acceleration also triples.
Acceleration decreases to one third.
If you triple the force acting on triple the mass, no change in acceleration is produced. Acceleration remains the same.
The acceleration of an object is always in the direction of the net force.
Acceleration is the ratio of force/mass. A heavy body has the same ratio as a lighter body, hence both accelerate equally in free fall.
6 N; 0 N.
Frontal area of fall and speed.
Zero.
A heavy parachutist must fall faster for air drag to build up to the chutist's greater weight (which is why the heavy parachutist has a
greater terminal speed).
The faster one encounters greater air resistance.
Two.
Yes.
Equal forces on unequal masses produce unequal accelerations, in accord with Newton's second law.
2
a = F/m = 200 N/40 kg = 5 m/s .
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The acceleration of each is the same: a = F/m = 2 N/2 kg = 1 N/1 kg = 1 m/s . (Incidentally, from the definition that 1 N = 1 kg.m/s ,
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you can see that 1 N/kg is the same as 1 m/s .)
2
For the jumbo jet: a = F/m = 4(30,000 N)/30,000 kg = 4 m/s .
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Net force (downward) = ma = (80 kg)(4 m/s ) = 320 N. Gravity is pulling him downward with a force of (80 kg)(10 m/s ) = 800 N, so
the upward force of friction is 800 N – 320 N = 480 N.
Acceleration will be g/2. From a = F/m = (W - R)/m = (W - W/2)/m = (W/2)/m = W/(2m). Since W/m = g, we see W/(2m) = g/2.
F = ma = mDv/Dt = (0.003 kg)(25 m/s)/(0.05 s) = 1.5 N, which is about 1/3 pound.
2
The wall pushes on you with 30 N. a = F/m = 30 N/60 kg = 0.5 m/s .