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The position vector  r of a particle of mass m is given by the following equation r(t)=αt3i^+βt2j^ , where  α=103ms3  , β=5ms2  and m=0.1 kg. At t=1 s, which of the following statement (s) is (are) true about the particle?

a
The velocity v→ is given by  v→=10i^+10j^ms−1
b
The angular momentum L→  with respect to the origin is given by  L→=−5/3k^Nms
c
The force  F→ is given by  F→=i^+2j^N
d
The torque  τ→ with respect to the origin is given by  τ→=−20/3k^Nm

detailed solution

Correct option is A

r→ =αt3i^+βt2j^→1Velocity, v→=dr→dt=3αt2i^+2βt j^→2Acceleration, a→=dv→dt=6αti^+2βj^→3 At t=1sec From (2): v¯=3αi^+2βj^=10i^+10j^=r→×v→mL→=αt3i^+βt2j^×3αt2i^+2βt j^0.1⇒L→=2αβt4k^−3αβt4k^0.1=0.1αβt4−k^=−53t4k^→4 At t=1=−53k^The force F→=ma→From (3), F→=0.120i^+10j^  =2i^+j^=dL→dt=203t3−k^=−203k^

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