Transcript B) component forces

Chapter 4
Pretest
1. A body is NOT in equilibrium
if:
A) it is moving at constant speed
in a straight line,
B) there is an unbalanced force
acting on the body,
C) it is at rest,
D) its motion is unchanged.
1. A body is NOT in equilibrium
if:
A) it is moving at constant speed
in a straight line,
B) there is an unbalanced
force acting on the body,
C) it is at rest,
D) its motion is unchanged.
2. Resolution of forces is
the procedure for finding:
A) parallel forces,
B) component forces,
C) equilibrant forces,
D) resultant forces.
2. Resolution of forces is
the procedure for finding:
A) parallel forces,
B) component forces,
C) equilibrant forces,
D) resultant forces.
3. Friction is a disadvantage:
A) in walking along a
sidewalk,
B) in automobile brakes,
C) in roller bearings on freight
cars,
D) between bike tires and the
dirt trail.
3. Friction is a disadvantage:
A) in walking along a
sidewalk,
B) in automobile brakes,
C) in roller bearings on
freight cars,
D) between bike tires and the
dirt trail.
4. Which of the following
statements about friction is FALSE?
Friction:
A) involves objects that are in
physical contact,
B) is less if surfaces are very
smooth,
C) is a force that resists motion,
D) is caused by uneven surfaces of
touching objects.
4. Which of the following
statements about friction is FALSE?
Friction:
A) involves objects that are in
physical contact,
B) is less if surfaces are very
smooth,
C) is a force that resists motion,
D) is caused by uneven surfaces of
touching objects.
5. A box is pulled along a level floor
at constant speed by a rope that
makes a 45 degree angle with the
floor. The box weighs 100 N. The
coefficient of sliding friction is 0.75.
The force exerted on the rope is:
A) 75 N,
B) between 75 N and 100 N,
C) 100 N,
D) greater than 100 N.
5. A box is pulled along a level floor at constant speed by a rope that
makes a 45 degree angle with the floor. The box weighs 100 N. The
coefficient of sliding friction is 0.75. The force exerted on the rope is:
A) 75 N,
B) between 75 N and 100 N,
C) 100 N,
D) greater than 100 N.
The correct answer is 60.6 N. The
writer of this question forgot to allow
for the decrease of the normal force
due to the upward component of
the force on the rope. Even the
eggheads make mistakes!
6. What causes a moving
object to change
direction?
a. acceleration
b. velocity
c. inertia
d. force
6. What causes a moving
object to change
direction?
a. acceleration
b. velocity
c. inertia
d. force
7. Which of the following is
the tendency of an object to
maintain its state of
motion?
a. acceleration
b. inertia
c. force
d. velocity
7. Which of the following is
the tendency of an object to
maintain its state of
motion?
a. acceleration
b. inertia
c. force
d. velocity
8. A wagon with a weight of
300.0 N is accelerated across
a level surface at 0.5 m/s2.
What net force acts on the
wagon?
a. 9.0 N
b. 15 N
c. 150 N
d. 610 N
8. A wagon with a weight of
300.0 N is accelerated across
a level surface at 0.5 m/s2.
What net force acts on the
wagon?
a. 9.0 N
b. 15 N
c. 150 N
d. 610 N
9. The statement by Newton
that for every action there is an
equal and opposite reaction is
which of his laws of motion?
a. first
b. second
c. third
d. fourth
9. The statement by Newton
that for every action there is an
equal and opposite reaction is
which of his laws of motion?
a. first
b. second
c. third
d. fourth
10. The magnitude of the
force of gravity acting on
an object is:
a. frictional force
b. weight
c. inertia
d. mass
10. The magnitude of the
force of gravity acting on
an object is:
a. frictional force
b. weight
c. inertia
d. mass
1. Define
equilibrium. What
conditions are
required for
equilibrium?
Equilibrium exists
when the net
force on an object
is zero. There is
no acceleration.
2. On point 0, a force of
25.0 N acts eastward and
a force of 10.0 N acts
southward. Calculate the
magnitude and direction of
the resultant force.
2
25
2
10
2
c
+
=
c = 27 N
tanq = 10/25
22° south of east
3. A carton weighing 250 N is
resting on a ramp that makes an
angle of 20.0° with the
horizontal. What are the
magnitudes of the components
of the weight of the carton
parallel to the ramp and
perpendicular to it?
The parallel component FII is
the opposite and the
perpendicular component F^
is the adjacent.
sin 20° = FII/250 N
FII = 85.5 N
cos 20° = F^/250 N
F^ = 235 N
4. If a steel block weighing
4.63 N can be pulled at a
constant speed across a
smooth steel plate by a
force of 2.64 N, what is
the coefficient of sliding
friction of steel on steel?
m = Ffriction/Fnormal
m = 2.64 N/4.63 N
m = 0.570
5. When a car is moving,
what happens to the
velocity and acceleration
of the car if the air
resistance becomes equal
to the force acting in the
opposite direction?
The acceleration
drops to zero, and
the velocity
becomes constant.
(This is the same principle
as terminal velocity.)
6. In a game of tug-of-war, a
rope is pulled to the left with
a force of 75 N and to the
right with a force of 102 N.
What is the magnitude and
direction of the net external
force on the rope?
102 N – 75 N =
27 N
to the right.