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Question: Answered & Verified by Expert
A particle of mass m is dropped from a height h above the ground. At the same time another particle of the same mass is thrown vertically upwards from the ground with a speed of 2gh. If they collide head-on completely inelastically, the time taken for the combined mass to reach the ground, in units of hg is:
PhysicsCenter of Mass Momentum and CollisionJEE MainJEE Main 2020 (08 Jan Shift 2)
Options:
  • A 12
  • B 34
  • C 12
  • D 32
Solution:
1238 Upvotes Verified Answer
The correct answer is: 32

time for collision t1=h2gh
After t1
VA=0-gt1=-gh2
and VB=2gh-gt1=gh2-12
at the time of collision
pi=pf
mVA+mVB=2mVf
-gh2+gh2-12=2Vf
Vf=0

and height from ground

=h-12gt12=h-h4=3h4

so time ,

t=2×3h4g=32 hg

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