A particle of mass m is moving in time t on a trajectory given by, r → = 10 α t 2 i ^ + 5 β…

A particle of mass m is moving in time t on a trajectory given by, 

r=10αt2i^+5βt-5j^

where α and β are dimensional constants.

The angular momentum of the particle becomes the same as it was for t=0 at time t=_____ seconds.

Solution

r=10αt2i^+5βt-5j^

v=20α+i^+5βj^

L=mr×v

=m10αt2i^+5βt-5j^×20αi^+5βj^

L=m50αβt2k^-100αβt2-5tk^

At t=0, L=0

50αβt2-100αβt2-5t=0

t-2t-5=0

t=10 sec

Asked in: JEE Main 2021 (25 Jul Shift 1)

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