Solving problems in physics generally requires
a few basic but essential steps.
Read the question carefully and decide nature of the answer.
What are we asked to find? Mass, velocity,
displacement, force, etc.
Write down the symbol for the answer with a question
mark. For example: m = ?, v = ?, d =? or f = ?
Reread the question to find out what information is given.
Record each bit of information as the problem is read.
For example: vo = 2.0 m/s, t = 3.0 sec, vf = 5.4 m/s, etc.
Notice that the units are included with each value. Units can
often be used to decide the nature of each value even if
you are not told directly in the problem what the number
value represents. For example: m/s must velocity or speed,
newtons must a force, seconds must be time, etc.
Unit systems are specified as MKS* (larger metric units),
CGS (smaller metric units) and English units.
Working with units generally requires us to stay in the
Same unit group for all values used in solving a problem.
For example: we would not use newtons (an MKS unit)
with grams (CGS). We would convert grams to kilograms
in order to use it with newtons.
Similarly, cm/ sec (CGS) would not be used with meters
(MKS), hours would not be used with seconds.
The MKS unit system is also called SI units.
Units of Commonly used Systems
MKS CGS English
Distance Meters (m) centimeters (cm) feet (ft)
Mass Kilogram (kg) gram (g) slug(sg)
Seconds (s) Seconds (s) Seconds (s)Time
Meter/ sec centimeter/ sec feet/ sec
(m/s) (cm/s) (ft/s)
Meter/ sec2 centimeter/ sec2 feet/ sec2
(m/s2) (cm/s2) (ft/s2)
force newtons (N) dynes(dn) pound (lb)
Units of Commonly used Systems (cont’d)
MKS CGS English
energy Kilojoules (Kj) ergs(er) foot pound (ft-lb)
power Kilowatt (Kw) watt(w) horsepower (hp)
Kilojoules joules calories
(Kj) (j) (cal)
Newton x sec dyne x sec pound x sec
(N x s) (dn x s) (lb x s)
Kilogram x m/sec gram x cm/sec slug x ft/sec
Kg x m/s g x cm/s sg x ft/s
Newton x meter dyne x centimeter foot x pound
N x m dn x cm ft x lb
More Commonly Used Units
Degrees radians revolutions
Revolutions per second (rps) hertzs (hz)
Seconds / revolution
Radians / second
Radians / second2
After identifying all the information given in the problem and
Deciding on what is to be found, the next step is to select an
Equation containing the unknown value.
Next, see if the selected equation contains all the variables that
are given in the problem. If so, insert the number values in
the appropriate spots in the equation and solve.
If the data for one of the required variables for solving
the equation is missing search the other available equations for
one that contains the missing variable and known data.
This equation will allow you to find the missing variable
value. Calculate its value and insert it into the equation
containing the unknown and solve for the answer.