Laws of Motion 5 Question 4

4. Two particles of mass m each are tied at the ends of a light string of length 2a. The whole system is kept on a frictionless horizontal surface with the string held tight so that each mass is at a distance a from the centre P (as shown in the figure). Now, the mid-point of the string is pulled vertically upwards with a small but constant force F. As a result, the particles move towards each other on the surface. The magnitude of acceleration, when the separation between them becomes 2x, is

(2007, 3M) (a) Obtain the relation between h and ω. What is the minimum value of ω needed, in order to have a non-zero value of h ?

(b) It is desired to measure g (acceleration due to gravity) using the set-up by measuring h accurately. Assuming that R and ω are known precisely and that the least count in the measurement of h is 104m, what is minimum possible error Δg in the measured value of g ?

(a) F2maa2x2

(b) F2mxa2x2

(c) F2mxa

(d) F2ma2x2x

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Answer:

Correct Answer: 4. (a)

Solution:

  1. As, from FBD (Free Body Diagram), 2Tcosθ=F

So,

T=F2secθ

Acceleration of particle

=Tsinθm=Ftanθ2m=F2mxa2x2



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