## Pages

### String, pully and spring

A lot of problems in mechanics involves string, pulley and springs for example masses are attached to string or spring and so on. Here are some concepts you need to remember while solving problems involving string, spring and pulleys.
(1) String
A. If not staded in the question consider the string to be inextensible.
B. Different blocks connected to an inextensible string would have same acceleration and for extensible string blocks would have different acceleration until the string can stretch.
C. Unless otherwise specified consider the string to be light i.e., consider its mass to be negligible in comparison to the block connected to it.
D. For a massless string tension in the string is zero although an ideal massless string is an practical impossibility.
E. Tension on different parts of the string would be different if string possess a considerable mass.

(2) Pulley
A. Unless or otherwise specified consider the pulley to be light having no effect on the system due to its weight.
B. The tension on strion on either side of pulley is taken to be same
C. If not specified consider the oulley to be frictionless in nature.

(3) Spring
A. Unless or otherwise specified consider the spring to be light and force constant of spring is same throughout whole length of the spring.
B. Spring has a elastic property that it can be compressed and stretched easily.
C. To stretch or compress a spring equal and opposite forces have to be applied at both the ends of the spring and in responce spring apply equal and opposite restoring force to bring the spring back to its natural position.
D For small compression and elongations this restoring force is given by Hook's Law which is
F=kx
where k is the spring constant and x is elongation or compression from the natural length of the spring.

So keep solving more and more physics problems Keeping these facts in mind. All the very best for your exams.

### IITJEE Tips and Tricks

Solve Force and motion problems easily
(1) First read the problem carefully.
(2) Determine which type of force is exerted in the system and where it is exertwd.
(3) See whether Newton's law of motion are applicable for the particular system or not i.e., see wherher frame of referance you are working with is inertial or non-inertial frame of refrence.
(4) Determine the system of units you have to use to solve a problem. If physical quantities in the question are given in different units then convert them to a convinent unit you want to work with generally S.I. system of unit is used in our text books.
(5) See if frictional forces are acting on the system if yes then take them into account.
(6) While taking care of friction forces see if they are static or kinetic in nature and accordingly work with them.
(6) Look for the direction of the frictional forces.
So keeping these simple points in mind you can solve force and motion problems easily