What constants should I know for physics? - MCAT

Not many. And those you need, you do not need with much precision at all.

• pi = 3 (Not kidding; this should be good enough. 3.1 in a pinch)
• sin(30) = 0.5; cos(30) = 0.9
• sin(45) = 0.7; cos(45) = 0.7
• sin(60) = 0.9; cos(60) = 0.5
• the speed of light in a vacuum (and air): c = 3 x 10^8m/s
• acceleration due to gravity near the surface of the Earth: g = 10 m/s^2
• the density of water, in the following units: 1000kg/m^3 = 1g/cm^3

Also useful:

• the speed of sound in air = 340 m/s
• 1 atmosphere = 100,000Pa = 10m of water = 760mmHg
• the density of water, in the following units: 1kg/L