Many of the students feel Physics as a difficult subject. Because, it involves many calculations, mathematical equations.
To solve the problems in Physics, it is essential to have knowledge of Algebra, Trigonometry, Calculus and integration.
Let me explain few steps to solve problems of physics When a problem is given to you,
# Read the question as many times you want, until you understand it.
# Try to recollect to which branch of the Physics it belongs i.e does it belong to Kinematics or heat or electricity.
# Note down every physical quantity involved in the question, including that physical quantity which has to be calculated in the question, with their symbols Ex: Time as(t); acceleration as (a);mass as (m) .
# Check whether all the physical quantities involved in the question, are in the same system of units C.G.S or F.P.S or S.I system of unit or not.
# If all the physical quantities are not in the same system of units, then convert them in to any one system i.e into either C.G.S or S.I systems of units.
# write an equation relating all the known physical quantities and the physical quantity which has to be determined in the equation.
# Substitute the values of all the physical quantities and constants in the equation.
# Solve the equation for the unknown physical quantity.
# After getting the result write the proper units.
Let me explain with few examples:
Ex 1) A person of mass 50kg in a lift. Calculate the apparent weight of the person when he moves ( i ) up with acceleration of 3 m/sec2 ( ii ) moves down with an acceleration of 4 m/sec2 ,( g = 10m/sec2 ).
Soln: After going through the problem, we can understand that the physical quantities involved in the problem are a)Mass of the person (m) = 50Kg ; b)acceleration of the lift (a) = 3 m/sec2
c) acceleration due to gravity (g) = 10m/sec2 , d) apparent mass of the person ( R ) =?
Part i) Now assume a formula which is connecting m,a,g and R . When the lift is moving up , R=m(g+a),as all the given physical quantities are in the same system of units i.e s.I system, we can directly substitute value in the above equation.
R = 50(10+3); R=50(13) R =650N.
ii) When the lift is moving down the formula to calculate apparent weight is R = m(g-a)
R=50(10-4); R=50(6) ; R=300N
Ex: 2) A 25kg block is in motion on a rough horizontal surface. A horizontal force of 75N is required to keep the body moving with constant speed. Find coefficient of kinetic friction. (g=10 m/)
Soln: After going through the question, we can understand that the physical quantities in the problem are a) =75N, m=25kg,g=10m/, =?
This is a problem of friction, the formula for co-efficient
Of kinetic friction = =
= = 0.3