Anytime when we solve physics problems we need to use all the variables in the same system of units.
It is more convenien to use International System of Units (SI units).
When you solve physics problems: remember to check the units before you substitute all the numbers into the equations.
All variables should be in SI units.
International System of Units (SI):

length 

mass 

time 

electric current 

temperature 


velocity 

acceleration 
meter per second squared,

force 
newton,

pressure 
pascal,

energy 
joule,

power 
watt,

electric charge 
coulomb,

electric potential 
volt,

capacitance 
farad,

electic resistance 
ohm,

inductance 
henry,

Unit Conversion:
1 mile = 1609.344 meter (m) 
1 meter (m) = 0.0006214 mile 
1 inch (in) = 0.0254 meter (m) 
1 meter (m) = 39.37 inch (in) 
1 foot (ft) = 12 inch (in) 
1 inch = 0.083 foot (ft) 
1 foot (ft) = 0.3048 meter (m) 
1 meter (m) = 3.28 foot (ft) 
1 meter/second (m/s) =
.................3.6 kilometer/hour (km/h) 
1 kilometer/hour (km/h) =
................0.2778 meter/second (m/s) 
1 mile/hour (mph) =
..........................0.447 meter/second (m/s) 
1 meter/second (m/s) =
.............2.24 mile/hour (mph) 
1 kilogram (kg) = 2.2046 pound (lb) 
1 pound (lb) = 0.4536 kilogram (kg) 
Temperature 
T (Kelvin) = T (Celsius) + 272.15 
T (Celsius) = T (Kelvin)  272.15 
T (Celsius) = (5/9)* [ T (Fahrenheit)  32 ] 
T (Fahrenheit) = (9/5)* T (Celsius) + 32 
You can find more unit conversion here:
www.unitconversion.info
Here you can find the physics problems on unit conversion: Problems.
