Centre of Mass 4 Question 6

7. Two point masses m1 and m2 are connected by a spring of natural length l0. The spring is compressed such that the two point masses touch each other and then they are fastened by a string. Then the system is moved with a velocity v0 along positive x-axis. When the system reaches the origin the string breaks

(t=0). The position of the point mass m1 is given by

x1=v0tA(1cosωt) where A and ω are constants.

Find the position of the second block as a function of time. Also, find the relation between A and l0.

(2003,4 M)

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Answer:

Correct Answer: 7. x2=v0t+m1m2A(1cosωt),l0=m1m2+1A

Solution:

  1. (a)

v=10m/s

x1=v0tA(1cosωt)xCM=m1x1+m2x2m1+m2=v0tx2=v0t+m1m2A(1cosωt)a1=d2x1dt2=ω2Acosωt

The separation x2x1 between the two blocks will be equal to l0 when a1=0

or cosωt=0

x2x1=m1m2A(1cosωt)+A(1cosωt) or l0=m1m2+1A(cosωt=0)

Thus, the relation between l0 and A is,

l0=m1m2+1A



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