Chapter 2: Newton’s Laws
TRUE/FALSE
1. All forces have specific directions associated with them.
2. “Net force” means the vector sum of all the individual forces acting on a particular body.
3. The weight of an object equals its mass times the acceleration of gravity.
4. You are presently exerting a gravitational force on the earth.
5. When a car goes around a curve of smaller and smaller radius, the centripetal force on it
decreases.
6. When a car goes around a curve at twice the speed, the centripetal force on the car doubles.
7. You roll a ball off a table and at the same time drop a second ball straight down from the
edge of the table. The second ball reaches the ground before the first ball.
8. With a fixed force, you will impart the same acceleration to a body on the earth and on the
moon.
9. When a body moves with uniform acceleration, the net force on it is zero.
10. You throw a ball straight up, it peaks out and then comes back down to you. During this
motion, the velocity and acceleration always point in the same direction.
11. During its entire motion, the acceleration of a projectile is always g.
12. At the peak of its motion, the acceleration of a projectile is zero.
13. As a projectile moves its speed stays constant while its direction changes.
14. When an object reaches its terminal speed, its acceleration is zero.
15. As an object moves faster through the air, its terminal speed increases.
16. The net force on the body has its largest magnitude.
17. The net force points downward.
18. The acceleration is zero.
19. The velocity points down.
20. The displacement vector from the equilibrium position has its largest magnitude.
21. The displacement vector from the equilibrium position points up.
22. When a body moves in a straight line with increasing speed, the net force on it must be
increasing.
23. To hold a 5 lb bag of sugar in your hand, you must push upwards on it with a force of 5 lb.
This is an example of Newton’s third law.
24. You push on a wall, and the wall pushes back on you with the same force. This is an
example of Newton’s third law.
25. When you jump, you accelerate upward because the floor exerts an upward force on you.
26. A newton is larger than a pound.
27. As you go higher and higher above the surface of the earth, the mass of a body stays
constant.
28. A body on the surface of the earth weighs 400 lb. The radius of the earth is about 4,000
miles. If this same body were placed on a 4,000 mile high tower, its weight would be 200 lb.
29. If a body were in orbit very near the surface of the earth, its centripetal acceleration would
be equal to g.
30. Planetary orbits are circles.
31. Just above the surface of the earth, the direction of the gravitational field is away from the
earth.
32. The direction of a field line at a point in space shows the direction of the force that would
act on a body placed at the point.
33. As you go from a point where a gravitational field is strong to a point where the
gravitational field gets weaker, the gravitational field lines get farther apart.
34. Gravity acts over a limited distance range.
35. Tides are caused because different parts of the earth’s oceans are at different distances from
the moon.
36. As an artillery shell travels from the gun to the target, the projectile’s vertical speed
changes, but it’s horizontal speed stays constant.
37. An aircraft weighing 1,500 N is accelerated at 15 m/s2 , the force acting on the aircraft is
2,295.9 N.
2295.9 N
38. An aircraft weighing 1,500 N has a mass of 153 kg..
39. A satellite orbiting the Earth in a circular orbit at 400 miles from the center of Earth is
moved to a distance of 1,200 miles from the center of Earth. The gravitational force
between the Earth and satellite changes by a factor of 3.
40. A ball on a string is being whirled around overhead when the string breaks. The ball will
move in the direction of the centripetal force the moment the string breaks.
MULTIPLE CHOICE
1. The acceleration of a body is
a.
always in the same direction as its velocity
b.
always in the same direction as the net force on the body
c.
in the direction that the body is moving
d.
equal to the net force on the body
e.
none of the above
2. An example of an action at a distance force is
a.
tension
b.
weight
c.
static friction
d.
kinetic friction
e.
none of the above
3. The SI units of velocity are
a.
mi/h
b.
km/h
c.
m/s2
d.
m/s
e.
none of the above
4. The SI units of acceleration are
a.
mi/h
b.
km/h
c.
m/s
d.
m/s2
e.
none of the above
5. The force needed to make an object move in a circle is
a.
centripetal force
b.
weight
c.
kinetic friction
d.
static friction
e.
none of the above
6. The force that keeps your feet from sliding as you walk is
a.
centripetal force
b.
weight
c.
kinetic friction
d.
static friction
e.
none of the above
7. If the net force on an object is zero,
a.
there must be no forces acting on the object
b.
the object must be at rest
c.
the object’s acceleration must be zero
d.
there can be no friction acting on the object
8. Which is larger, a newton or a pound?
a.
a newton
b.
a pound
c.
This question is nonsense—they don’t measure the same physical quantity.
d.
They are the same size.
9. You push on a block on frictionless ice with a force of 8 N, causing it to accelerate at 2 m/s2.
The mass of the block is
a.
2 kg
b.
4 kg
c.
8 kg
d.
16 kg
e.
6 kg
10. Starting from rest, a 2 kg body acquires a speed of 8 m/s in 2 seconds. The net force acting
on the body is
a.
2 N
b.
4 N
c.
8 N
d.
16 N
e.
6 N
11. Two forces of 4 N and 12 N act on a body simultaneously. The net force on the body is
a.
4 N
b.
12 N
c.
16 N
d.
8 N
e.
impossible to tell from the given information
12. You whirl a 2 kg body attached to a 1 meter cord around your head in a nearly horizontal
circle with a speed of 4 m/s. The tension in the cord is
a.
2 N
b.
4 N
c.
8 N
d.
16 N
e.
32 N
13. If object A has more mass than object B,
a.
A will weigh more than B.
b.
A will be harder to accelerate than B.
c.
A will be harder to keep moving in a circle.
d.
all of the above
14. The frequency of a body oscillating from a spring on the moon is___________ the
frequency of the same body oscillating from the same spring on earth.
a.
the same as
b.
larger than
c.
smaller than
d.
not related to
e.
depending on the mass, smaller or larger than
15. Two identical cars are traveling around the same curve on a highway. One of them is
moving at 60 mph, and the other is moving at 30 mph. The centripetal force acting on the
car moving at 60 mph is __________ the value of the centripetal force acting on the car
moving at 30 mph.
a.
one quarter
b.
one half
c.
the same as
d.
twice
e.
four times
16. A car moving at a constant speed goes around a curve of 400 ft radius and then goes around
a second curve of 200 ft radius. The centripetal force acting on the car as it goes around the
200 ft radius curve is ___________ the value of the centripetal force acting on the car as it
goes around the 400 ft radius curve.
a.
one quarter
b.
one half
c.
the same as
d.
twice
e.
four times
17. You roll a ball off a table and at the same time drop a second ball straight down from the
edge of table. The second ball reaches the ground ____________ the first ball reaches the
ground.
a.
before
b.
at the same time that
c.
after
d.
before or after, depending on the masses,
e.
cannot be determined
18. When a freely falling object reaches its terminal speed,
a.
it is still accelerating
b.
its acceleration is zero
c.
it is decelerating
d.
its acceleration cannot be determined
19. The elevator is accelerating upwards at 2 ft/s2.
a.
150 lb
c.
170 lb
b.
160 lb
d.
none of the above
20. The elevator accelerates upwards and is now moving at a constant speed.
a.
150 lb
c.
170 lb
b.
160 lb
d.
none of the above
21. After moving upwards at constant speed, the elevator is slowing down at 2 m/s2 as it is
coming to rest.
a.
150 lb
c.
170 lb
b.
160 lb
d.
none of the above
22. The elevator is accelerating downwards at 2 ft/s2.
a.
150 lb
c.
170 lb
b.
160 lb
d.
none of the above
23. The elevator accelerates downwards and is now moving at a constant speed.
a.
150 lb
c.
170 lb
b.
160 lb
d.
none of the above
24. After moving downwards at constant speed, the elevator is slowing down at 2 m/s2 as it is
coming to rest.
a.
150 lb
c.
170 lb
b.
160 lb
d.
none of the above
25. The elevator cable breaks.
a.
150 lb
c.
170 lb
b.
160 lb
d.
none of the above
26. You throw a ball straight up, it peaks out, and then comes back down to you. During this
motion, the velocity and acceleration
a.
always point in the same direction
b.
always point opposite to each other
c.
sometimes point in the same direction, and other times point opposite to each other
d.
depend on the way the ball is thrown
e.
depend on the mass of the ball
27. The horizontal speed of a projectile
a.
is zero
b.
stays constant
c.
continuously increases
d.
continuously decreases
e.
sometimes decreases and sometimes increases
28. The vertical speed of a projectile
a.
is zero
b.
stays constant
c.
continuously increases
d.
continuously decreases
e.
sometimes decreases and sometimes increases
29. The horizontal acceleration of a projectile
a.
is zero
b.
stays constant
c.
continuously increases
d.
continuously decreases
e.
sometimes decreases and sometimes increases
30. The vertical acceleration of a projectile
a.
equals g pointing downwards
b.
equals g pointing upwards
c.
equals g pointing sometimes upwards and other times downwards
d.
is zero
e.
continuously increases
31. Planetary orbits are
a.
parabolas
c.
circles
b.
ellipses
d.
none of the above.
32. Where is the sun located relative to a planet’s orbit about it?
a.
at the center of the orbit, which is a circle
b.
at the center of the orbit, which is an ellipse
c.
at one focus of the ellipse which forms the orbit
d.
none of the above
33. At the highest point on the path of a projectile, its vertical acceleration
a.
equals g pointing downwards
b.
equals g pointing upwards
c.
is zero
d.
is undetermined
e.
does not exist
34. As a body falls through air starting from rest, its acceleration
a.
is zero
b.
stays constant
c.
continuously decreases
d.
continuously increases
e.
gets smaller and smaller, eventually approaching zero
35. As a body falls through air starting from rest, its velocity
a.
stays constant
b.
continuously decreases
c.
continuously increases
d.
gets larger and larger, eventually reaching a constant value
e.
gets smaller and smaller, eventually approaching zero
36. Suppose I push lightly on the chair, and the chair doesn’t move at all. Then the strength of
the force the chair exerts on me is
a.
less than the force I exert on the chair
b.
equal to the force I exert on the chair
c.
greater than the force I exert on the chair
d.
zero
37. Suppose I push moderately on the chair, and this time the chair does move. Then the
strength of the force the chair exerts on me is
a.
less than the force I exert on the chair
b.
equal to the force I exert on the chair
c.
greater than the force I exert on the chair
d.
zero
38. Suppose I push very hard on the chair, and this time the both the chair moves and I slip
backward as well. Then the strength of the force the chair exerts on me is
a.
less than the force I exert on the chair
b.
equal to the force I exert on the chair
c.
greater than the force I exert on the chair
d.
zero
39. The velocity
a.
is zero
c.
points up
b.
has its largest magnitude
d.
points down
40. Two cars crash head on. At any given time during the crash, the magnitudes of the collision
forces exerted on each car are exactly equal. This is an example of Newton’s
a.
first law
c.
third law
b.
second law
d.
no law
41. A heavy truck hits a small car. At any given time during the impact,
a.
the force the truck exerts on the car is larger than the force the car exerts on the
truck
b.
the force the truck exerts on the car is smaller than the force the car exerts on the
truck
c.
the force the truck exerts on the car is equal to the force the car exerts on the truck
d.
the only force present is the force of the truck on the car
42. As a space shuttle is launched into orbit, the direction of its acceleration
a.
always points upward
b.
always points downward
c.
varies between pointing upward and pointing downward
d.
stays constant
43. Which statement is incorrect? The gravitational force on an orbiting satellite due to the
earth
a.
aims toward the center of the earth
b.
depends on the earth’s mass
c.
depends on the satellite’s mass
d.
depends on the distance between the earth and the satellite
e.
none of the above
44. A body on the surface of the earth weighs 400 lb. The radius of the earth is about 4,000
miles. If this same body were placed on a 4,000 mile high tower, its weight would be
a.
100 lbs
b.
200 lbs
c.
400 lbs
d.
800 lbs
e.
16,000 lbs
45. The symbol G is used to represent
a.
the acceleration of gravity
b.
the universal gravitational constant