80. Average speed, as opposed to average velocity, relates to the total distance, as opposed to the net

displacement. The distance D up the hill is, of course, the same as the distance down the hill, and since
the speed is constant (during each stage of the motion) we have speed = D/t. Thus, the average speed
is

D

up

+ D

down

t

up

+ t

down

=

2D

D

v

up

+

D

v

down

which, after canceling D and plugging in v

up

= 4 0 km/h and v

down

= 60 km/h, yields 48 km/h for the

average speed.

Document Outline

• Main Menu
• Chapter 1 Measurement
• Chapter 2 Motion Along a Straight Line
  • 2.1 - 2.10
    • 2.1
    • 2.2
    • 2.3
    • 2.4
    • 2.5
    • 2.6
    • 2.7
    • 2.8
    • 2.9
    • 2.10
  • 2.11 - 2.20
    • 2.11
    • 2.12
    • 2.13
    • 2.14
    • 2.15
    • 2.16
    • 2.17
    • 2.18
    • 2.19
    • 2.20
  • 2.21 - 2.30
    • 2.21
    • 2.22
    • 2.23
    • 2.24
    • 2.25
    • 2.26
    • 2.27
    • 2.28
    • 2.29
    • 2.30
  • 2.31 - 2.40
    • 2.31
    • 2.32
    • 2.33
    • 2.34
    • 2.35
    • 2.36
    • 2.37
    • 2.38
    • 2.39
    • 2.40
  • 2.41 - 2.50
    • 2.41
    • 2.42
    • 2.43
    • 2.44
    • 2.45
    • 2.46
    • 2.47
    • 2.48
    • 2.49
    • 2.50
  • 2.51 - 2.60
    • 2.51
    • 2.52
    • 2.53
    • 2.54
    • 2.55
    • 2.56
    • 2.57
    • 2.58
    • 2.59
    • 2.60
  • 2.61 - 2.70
    • 2.61
    • 2.62
    • 2.63
    • 2.64
    • 2.65
    • 2.66
    • 2.67
    • 2.68
    • 2.69
    • 2.70
  • 2.71 - 2.80
    • 2.71
    • 2.72
    • 2.73
    • 2.74
    • 2.75
    • 2.76
    • 2.77
    • 2.78
    • 2.79
    • 2.80
  • 2.81 - 2.90
    • 2.81
    • 2.82
    • 2.83
    • 2.84
    • 2.85
    • 2.86
    • 2.87
    • 2.88
    • 2.89
    • 2.90
  • 2.91 - 2.100
    • 2.91
    • 2.92
    • 2.93
    • 2.94
    • 2.95
    • 2.96
    • 2.97
    • 2.98
    • 2.99
    • 2.100
  • 2.101 - 2.110
    • 2.101
    • 2.102
    • 2.103
    • 2.104
    • 2.105
    • 2.106
    • 2.107
    • 2.108
    • 2.109
    • 2.110
• Chapter 3 Vectors
• Chapter 4 Motion in Two and Three Dimensions
• Chapter 5 Force and Motion I
• Chapter 6 Force and Motion II
• Chapter 7 Kinetic Energy and Work
• Chapter 8 Potential Energy and Conservation of Energy
• Chapter 9 System of Particles
• Chapter 10 Collisions
• Chapter 11 Rotation
• Chapter 12 Rolling, Torque, and Angular Momentum
• Chapter 13 Equilibrium and Elasticity
• Chapter 14 Gravitation
• Chapter 15 Fluids
• Chapter 16 Oscillations
• Chapter 17 Waves—I
• Chapter 18 Waves—II
• Chapter 19 Temperature, Heat, and the First Law of Thermodynamics
• Chapter 20 The Kinetic Theory of Gases
• Chapter 21 Entropy and the Second Law of Thermodynamics
• Chapter 22 Electric Charge
• Chapter 23 Electric Fields  
• Chapter 24 Gauss’ Law
• Chapter 25 Electric Potential
• Chapter 26 Capacitance
• Chapter 27 Current and Resistance
• Chapter 28 Circuits
• Chapter 29 Magnetic Fields
• Chapter 30 Magnetic Fields Due to Currents
• Chapter 31 Induction and Inductance
• Chapter 32 Magnetism of Matter: Maxwell’s Equation
• Chapter 33 Electromagnetic Oscillations and Alternating Current
• Chapter 34 Electromagnetic Waves
• Chapter 35 Images
• Chapter 36 Interference
• Chapter 37 Diffraction
• Chapter 38 Special Theory of Relativity
• Chapter 39 Photons and Matter Waves
• Chapter 40 More About Matter Waves
• Chapter 41 All About Atoms
• Chapter 42 Conduction of Electricity in Solids
• Chapter 43 Nuclear Physics
• Chapter 44 Energy from the Nucleus
• Chapter 45 Quarks, Leptons, and the Big Bang