## 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.