MOVING COORDINATE SYSTEM
The 8th
Routine Task
A.
READING QUIZ
1.
In
dynamics, the friction force acting on a moving object is always
a.
In
the direction of its motion
b. A
kinetic friction
c.
A
static friction
d.
Zero
Answer : b. A kinetic Friction
The friction force acting on a moving object is
known as a kinetic friction. It’s different with static friction, that is a
friction acts and an object remains stationary.
2.
If
a particle is connected to a spring, the elastic spring force is expressed by
F= ks. The “s” in this equation is the
a.
Spring
constant
b.
Un-deformed
length of the spring
c. Difference
between deformed length and un-deformed length
d.
Deformed
length of the spring
Answer : c.
Difference between deformed length and un-deformed length
A linear
spring develops a force according to F= ks (essentially the equation of a
line). The work of the spring force moving from position S1 to position S2, so
the equation is 
B.
CONCEPT QUIZ
1.
If
the cable has a tension of 3N, determine the acceleration of block B.
a.
4.26
m/s2 ↑
b.
4.26
m/s2 ↓
c.
8.31
m/s2 ↑
d. 8.31
m/s2↓
Answer :
∑F = maB
2T – WB = -4aB
2(3) – (4)(9.81) = - 4aB
-33.24 = -4aB
d. aB = 8.31 m/s2
2.
Determine
the acceleration of the block
a.
2.20
m/s2 ↑
b.
3.17
m/s2 ↑
c.
11.0
m/s2↑
d.
4.26
m/s2 ↑
C.
ATTENTION QUIZ
1.
Determine
the tension in the cable when the 400 kg box is moving upward with a 4 m/s2
acceleration
a.
2265
N
b.
3365
N
c. 5524
N
d.
6543
N
Answer:
c. 5524 N
No
matter what the angle is :
For
400kg mass of the box = T – 400 (9.8) = m . a
T
– 3920 = 400 . 4
T
– 3920 = 1600
T
= 1600 + 3920
T
= 5520 N
2.
A
10 Ib particle has forces of F1 = (3i + 5j ) Ib and F2 =
(-7i + 9j) Ib acting on it. Determine the acceleration of the particle
a. (-0.4
i + 1.4j) ft/s2
b.
(-4
i + 14j) ft/s2
c.
(-12.9
i + 45j) ft/s2
d.
(13i
+ 4j) ft/s2
Answer
: a. (-0.4 i + 1.4j) ft/s2
FR
= F1 + F2
FR
= (3i + 5j ) Ib + (-7i + 9j) Ib
=
(- 4i + 14j) Ib
a
= F/m
a
= (- 4i + 14j) Ib / 10
a
= (-0.4 i + 1.4j) ft/s2
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