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Byju's Answer

Standard XII

Physics

Displacement of COM:Application

Dear Sir/Mada...

Question

Dear Sir/Madam
I am unable to understand in questions, when to equate the forces and when to equate the work done by the respective forces in similar conditions.
Example: An object of mass m is suspended with an unstretched vertical spring. Whem mass m is just released after connecting to the spring, what is the masimum elongation of the spring?
In this question,
1. If I equate the net 'forces' acting on the mass after the total elongation i.e. mg= kx, I get x=mg/k
2. However if I equate the work done by gravitation force and spring force i.e. mgx=1/2kx^2, I get x = 2mg/x which is the answer.
Kindly help me understand when to equate forces and work done in such questions?

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Solution

whenever they refer to the word maximum elongation or maximum compression u should go for work-energy method....but if they have just asked for elongation you can use force equation method.

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Similar questions

Q. A block of mass

m

initially has a velocity

v_{0}

when it just touching a spring. The block moves through a distance

I

before it stops after compressing the spring. The spring constant is

k

and the coefficient of kinetic friction between block and table is

μ

. As the block moves the distance

l

(a) what is the work done on it by the spring force? Are there other forces acting on the block, and if so, what work do they do?
(b) what is the total work done on the block?
(c) use the work energy theorem to find the value of

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in terms of

v_{0}, μ, g

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Q. Two springs have force constants

k_{1}

and

k_{2} (k_{1} > k_{2})

. On which spring is more work done, if (i) they are stretched by the same force and (ii) they are stretched by same distance?

Two springs A and B have force constants $k_{1}$ and $k_{2}$ respectively. The ratio of work done on A to that done on B when they are stretched by the same force is

Q. If two springs

S_{1}

and

S_{2}

of force constants

k_{1}

and

k_{2}

respectively, are stretched by the same force, it is found that more work is done on spring

S_{1}

than on spring

S_{2}

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Statement-1: If stretched to the same extension, work done on

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Statement-2:

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Choose the correct option.

Describe when the work done by spring force will be positive and when it will be negative in a horizontal spring mass system

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