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## Solving a Physics Problem

Only two things are certain: the universe and human stupidity; and I'm not certain about the universe.
- Albert Einstein

So you want to know how to solve physics problems? Solving physics problems requires logic.

1. Find out all you can about the problem. Look for givens and assumptions.
2. Draw a representation. Mark all forces with their respective directions. Lable all figures.
3. Derive an equation using known equation.
4. Use math to simplify the problem and then solve the problem.
If that sounds complicated, we'll go through a simple physics problem. Lets say a block of wood is sitting on a inclined plane. How long will it take for the block to reach the bottom? What is the normal force of the block? The block of wood has a mass of 10 kg and its height is 2 m. The plane is inclined at 30 degrees and is frictionless.

Step I:

• m=10 kg
• h = 2m
• theta = 30
• ay=0 (in the new coordinate system)

Step II:

Step III:
Editors note: observe the turned axis. This makes the equations much easier to deal with
Fx = m ax = - mg sin theta = -98 sin 30 = 49 N (Newtons)
Fy = m ay = 0 = N (normal) - mg cos theta = N - 98 cos 30 = N - 8.49

Step IV:
First problem, how long will it take to reach the bottom?
m ax=49 N
ax = 49 N / m = 4.9 m/s2
x = ax t2
2 sin 30 = 4.9m/s2 t2
t2 = .2040
t = .45 seconds

Second problem, what is the normal?
m ay = 0 = N - mg cos theta = N - 8.49 N
N = 8.49