Fundamentos da termodinamica- exercicios resolvidos

2-1

CHAPTER 2
The correspondence between the problem set in this fifth edition versus the problem set in the 4'th edition text. Problems that are new are marked new and those that are only slightly altered are marked as modified (mod).
New
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20

Old
4 mod new new
7 mod
2 mod new new new 5 mod
6
8 mod new 9 mod
10 mod
11
new new 16 mod new 12

New
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39E
40E

Old
13
14
15
17
18
new
19
20
21
22
23
24 new 25 mod
26 mod
27 mod
28
29
31E mod
32E

New
41E
42E
43E
44E
45E
46E
47E
48E
49E

Old
33E mod
34E mod
35E
36E
37E
38E
39E
40E
41E

2-2
2.1

The “standard” acceleration (at sea level and 45° latitude) due to gravity is 9.80665 m/s2. What is the force needed to hold a mass of 2 kg at rest in this gravitational field ? How much mass can a force of 1 N support ?
Solution:
ma = 0 = ∑ F = F - mg
F = mg = 2 × 9.80665 = 19.613 N
F = mg

2.2

=>

m = F/g = 1 / 9.80665 = 0.102 kg

A model car rolls down an incline with a slope so the gravitational “pull” in the direction of motion is one third of the standard gravitational force (see Problem
2.1). If the car has a mass of 0.45 kg. Find the acceleration.
Solution:
ma = ∑ F = mg / 3 a = mg / 3m = g/3 = 9.80665 / 3 = 3.27 m/s2

2.3

A car drives at 60 km/h and is brought to a full stop with constant deceleration in 5 seconds. If the total car and driver mass is 1075 kg. Find the necessary force.
Solution:
Acceleration is the time rate of change of velocity. ma = ∑ F ;

a = dV / dt = (60 × 1000) / (3600 × 5) = 3.33 m/s2

Fnet = ma = 1075 × 3.333 = 3583 N
2.4

A washing machine has 2 kg of clothes spinning at a rate that generates an acceleration of 24 m/s2. What is the force needed to hold the clothes?
Solution:
F = ma = 2 kg × 24 m/s2 = 48 N

2.5

A 1200-kg car moving at 20 km/h is accelerated at a constant rate of 4 m/s2 up to a speed of 75 km/h. What are the force and total time required?
Solution:
a = dV / dt => ∆ t = dV/a = [ (