2.4 
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Interactive Simulations   Position and displacement in one dimension    Displacement and position in two dimensions    Solve v=dx/dt for dt    Velocity, position, and time (basic version)    Velocity, position, and time (more advanced version)    Acceleration (basic version)    Acceleration (more advanced version)    Static equilibrium    Static equilibrium and the lever    Newton's second law (basic version)    Newton's second law (more advanced version)    Circular motion interactive simulation    Orbits of the planets and dwarf planets    Orbits simulation Interactive Calculators   Speed calculator    Velocity calculator    Acceleration calculator    Velocity in accelerated motion    Average velocity calculator    Hooke's law calculator    Torque calculator    Rotational equilibrium and torque    Newton's second law calculator    Momentum calculator    Angular velocity    Linear velocity and angular velocity    Centripetal acceleration    Centripetal force    Law of universal gravitation calculator
1 - Science of Physics
2 - Forces and Motion      Chapter 2 at a glance      2.1 - Motion      2.2 - Force, momentum, and Newton's laws      2.3 - Circular motion      2.4 - Solving harder physics problems      2.5 - Chapter review3 - Energy Transformations4 - Waves and Sound
5 - Electricity and Magnetism
6 - Light and Optics
7 - The Atom
8 - Linear Motion
9 - Vectors and Forces
10 - Forces
11 - Newton's Laws and Gravitation
12 - Circular Motion and Gravitation
13 - Torque and Static Equilibrium
14 - Momentum and Collisions
15 - Angular momentum
16 - Power and Machines
17 - Harmonic Motion
18 - Waves
19 - Sound
20 - Electricity
21 - Electric and Magnetic Fields
22 - Electromagnetism and Induction
23 - Light and Color
24 - Geometrical Optics
25 - Electromagnetic Radiation
26 - The Properties of Matter
27 - Thermodynamics and Heat Transfer
28 - The Atom
29 - The Quantum Theory
30 - TBD
31 - TBD
32 - TBD
33 - TBD
34 - TBD
35 - TBD
36 - TBD
37 - The atomic nucleus and radioactivity
38 - Nuclear reactions
39 - Relativity
40 - Particle physics and the standard model
41 - Electronics (semiconductors)
42 - Nuclear technology
43 - Lasers and photonics
44 - Metals, alloys and materials science
45 - Communications technology
46 - Buildings and structures
47 - Energy technology
48 - Biophysics
49 - Matter and Energy, Space and Time
50 - Energy Transformations
51 - Nanotechnology
52 - Website Videos
53 - ExtraStuff
55 - Modeling Motion, Friction, and Center of Mass
56 - Work and the Conservation of Energy
Using equations
Why "solve" an equation? This problem asks for a time but the equation gives you a speed. How do you get the time? The answer is to "solve" the equation for time. "Solving for t" means to rearrange the equation into a form t = ? in which "?" are the other variables and there are no t's on the right hand side of the equal sign. Using the rules of algebra, we can restate the same relationship as t = d ÷ v or as d = vt.
Solving the speed equation for distance or time
How do I use the equation? The above equations are general which means they apply to generic situations so they have to be rewritten with the specific speed, time, and distance variables for your problem. Lets look at the equation for bicycle 1. We write the speed equation as d1 = v1t1. We do a similar thing for bicycle 2 to get a second equation d2 = v2t2.
Applying the general relationship to this particular problem
Is there enough information? We are given that v1 = 5 m/s. But, we do not know the distance, d1 so we cannot calculate a time. The equation for bicycle two has the same problem. This brings up an important rule.

One equation allows you to determine only one unknown value.
How do I know there is enough? Looking at this problem we see that there are four unknown values: t1, t2, d1 and d2. It is a rule that you need as many equations as you have unknown values. Four unknowns means we need four equations to solve the problem. We have two equations, we need two more.
Known and unknown quantities for this problem

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