Download Ch. 2 Equilibrium

Physics
Ch 2 Mechanical Equilibrium
Pre-Test
1. Which of the following statements does not describe force?
a. Force causes objects at rest to remain stationary.
b. Force causes objects to start moving.
c. Force causes objects to stop moving.
d. Force causes objects to change direction.
2. An object is at rest suspended from two cables. Which of the following properly describes the forces
involved?
a. The sum of forces acting upward on the c. The forces acting upward and downward
object are greater than the forces acting
on the object are balanced
downward
b. The sum of forces acting upward on the d. No forces are acting on the object
object are less than the forces acting
downward
3. The length of a force vector represents the
a. cause of the force.
b. direction of the force.
c. magnitude of the force.
d. type of force.
4. A single force acts on an object. The components of this force act along the +x-axis and the –y-axis. The
single force that will bring the object into equilibrium has components that act along the
a. +x-axis and +y-axis.
c. -x-axis and +y-axis.
b. +x-axis and -y-axis.
d. -x-axis and -y-axis.
5. What is the minimum resultant possible when adding a 5-N force to an 8-N force?
a. 5 N
b. 3 N
c. 8 N
d. 13 N
e. 40 N
6. A 100-N lantern is suspended by a pair of ropes with 120 degrees between them (each 60 degrees from the
vertical). The tension in each rope is
a. less than 100 N.
b. more than 100 N.
c. 100 N.
7. Which of the following descriptions best describes an object at rest on a table?
a. The support force is equal to the object’s c. The support force is less than the object’s
weight
weight
b. The support force is greater than the
d. There is not enough information here to
object’s weight
compare the support force to the weight
8. The Newton is the SI unit for what physical quantity?
a. static equilibrium
c. mass
b. force
d. dynamic equilibrium
9. What term is used to describe the vector sum of all forces acting on an object?
a. net force
c. support force
b. tension
d. equilibrium
10. Briefly distinguish between vectors and scalars, giving examples of each.
11. Describe/Identify all the forces acting on a crate that is being pulled at a constant speed across the floor
using a rope.
12. Phreddy Physics hangs at rest from two gymnast rings each supported by its own rope hanging vertically
from the ceiling. If Phreddy weighs 650 N, What is the tension in each of the ropes?
13. A window washing rig consists of scaffold supported at each end with 2 vertical cables. The cables each
have a breaking strength 5.0 x 103 Newtons. If the scaffold weighs 350 N, How much additional weight
can the rig support?
14. Two children push on a crate across a smooth floor (ignore friction). Child A pushes with 350 N of force
to the north. Child B pushes with 520 N of force to the East. What is the magnitude of the net force
acting on the crate?
Mechanical Equilibrium Pre-Test
Answer Section
MULTIPLE CHOICE
1.
2.
3.
4.
5.
6.
7.
8.
9.
ANS:
ANS:
ANS:
ANS:
ANS:
KEY:
ANS:
KEY:
ANS:
ANS:
ANS:
A
PTS:
C
PTS:
C
PTS:
C
PTS:
B
PTS:
force | resultant
C
PTS:
tension | rope
A
PTS:
B
PTS:
A
PTS:
1
1
1
1
1
1
DIF: I
OBJ: 4-1.1
DIF:
DIF:
DIF:
BLM:
DIF:
BLM:
OBJ: 4-1.2
OBJ: 4-2.3
OBJ: 2.1 Force
I
II
L2
application
L2
application
OBJ: 2.3 Support Force
1
1
1
ESSAY
10. ANS:
A vector is a quantity that has direction and magnitude; a scalar has only magnitude. Force, velocity, acceleration,
and weight are all vectors. Mass, time, temperature, and speed are scalars.
PTS: 1
DIF: L2
OBJ: 2.5 Vectors KEY: vector | scalar
BLM: comprehension
11. ANS:
Gravity exerts a downward force on the crate that is balanced by the normal force of the floor acting upward on the
crate. There is a tension force being applied to the crate from the rope in the direction of motion, and there is a
frictional force between the crate and the floor that acts in a direction opposite of the motion.
PTS: 1
DIF: II
OBJ: 4-2.2
PROBLEM
12. ANS:
325 N
PTS: 1
13. ANS:
Total weight that can be supported = 2 (5.0 x 103) N = 1.0 x 104 N. Since the scaffold weighs 350 N, that leaves 1.0
x 104 - 350 = 9650 N
9700 N
PTS: 1
14. ANS:
Apply Pythagorean Theorem...
F2 = 5202 + 3502
F = 626.8 = 630 N
PTS: 1