Chapter 4 5 Problems 202213.pdf - Chapter 4 5 : Forces –...

Chapter 4, 5 : Forces – Questions and Problems
PRACTICE WITH VECTORS, TO DO ON YOUR OWN
Exercise 1 : Three forces act on an object:
⃗
F
1
=
[
5.0
0.0
]
N
,
⃗
F
2
=
[
0.0
6.0
]
N
and
⃗
F
3
=
[
− 4.0
0.0
a) Draw a force diagram
b) Calculate the net force
Σ
⃗
c) Find the direction of the acceleration vector, ⃗ a . Add the acceleration vector to the diagram.
d) The three forces are applied for 5.0 seconds. Calculate the change in linear momentum, Δ ⃗
e) The three forces are applied for 10.0 seconds. Calculate the change in linear momentum, Δ ⃗
f) The three forces are applied for 2.0 seconds. The initial linear momentum is ⃗
p
i
=
[
0.0
10.0
]
kg.m /
. Calculate the final momentum,
⃗ p
f
. Draw the initial and final momenta on the diagram.
]
N
F
p
p
s
Answers:
[
1.0
6.0
]
N ;
[
5.0
30
]
kg.m / s;
[
10
60
]
kg.m / s;
[
2.0
22
]
kg.m / s
Exercise 2 : Draw a force-acceleration diagram in the following cases
a) A one-tonne elevator is pulled by an upward 30.0 kN tension force. (1 tonne = 1 000 kg)
b) A 203.9 kg car drives on a horizontal highway, to the right, at a constant speed. Air drag is 5.0
kN to the left.
Exercise 3 : Four forces are acting on an object :
⃗
F
1
=
[
5.0
− 2.0
]
N
⃗
F
2
=
[
− 3.0
2.0
]
⃗
F
3
=
[
− 6.0
2.0
]
N
⃗
F
4
=
[
− 2.0
1.0
]
N
a) Calculate the net force Σ
⃗
b) Draw a force acceleration diagram
c) Knowing that the initial momentum of the object is ⃗
p
i
=
[
5.0
0.0
]
kg.m / s
and the final momentum
is ⃗
p
f
=
[
− 13.0
9.0
]
kg.m / s
, calculate the time it took to change the momentum. Ans: 3.0 s.
Exercise 4 : A block (of mass 4.0 kg) is held using four forces of magnitudes
T
1
= 10.0 N ;T
2
= 12.0 N ; T
3
= 8.80 N
and
T
4
.
⃗
T
3
is horizontal.
a) What is the net force acting on the block, in terms of
T
4
b) Calculate
⃗
T
4
c) Calculate
T
4
and the direction angle of
⃗
T
4
N
F
?
.
.
o
1

Chapter 4, 5 : Forces – Questions and Problems
CONCEPTUAL QUESTIONS TO DO ON YOUR OWN (REVIEW)
#C3 . Is inertia always the same thing as mass?
#C4 . What is weight?
#C5. Which is correct?