Q4 of 21 Page 109

Two identical small bodies each of mass m and charge q are suspended from two strings each of length l from a fixed point. The whole system is taken into an orbiting artificial satellite. Find the tension in strings

Given:

Two identical small bodies are having mass = m and charge = q and suspended by a string of length l.


The bodies can experience three forces:


(1) Electrostatic Forces


(2) Gravitational Force


(3) Tension


The tension in the string balances the other two forces to maintain equilibrium.


Now, the system is taken to an artificial orbital satellite. Now, we already know that the gravitational force is very smaller than the electrostatic force.


In the outer space, the gravitational pull of the earth is almost negligible due to large distance.


So, now the tension is only balancing electrostatic force.


Since both bodies are identical and have the same charge, so they repel each other, such that they both make 180° with each other.


The distance between them is l + l = 2l



Now, Tension = Electrostatic Repulsion =


So, Tension = where k =


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2

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 3

Two blocks of masses 2kg and 4kg are hanging with the help of a massless string passing over an ideal pulley inside an elevator. The elevator is moving upward with an acceleration g/2. The tension in the string connected between the blocks will be (take g = 10 ms–2)

a) 40N


b) 60N


c) 80N


d) 20N

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(a) What is the weight shown by the machine?


(b) What force should the man exert on the rope to get his correct weight on the machine?

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