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.
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.
- Find out all you can about the problem. Look for givens and assumptions.
- Draw a representation. Mark all forces with their respective directions. Lable all figures.
- Derive an equation using known equation.
- Use math to simplify the problem and then solve the problem.
- m=10 kg
- h = 2m
- theta = 30
- ay=0 (in the new coordinate system)
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
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