Kinematics 6 Question 9

9. Two vectors A and B are defined as A=ai^ and B=a(cosωti^+sinωtj^), where a is a constant and ω=π/6 rad s1. If |A+B|=3|AB| at time t=τ for the first time, the value of τ in seconds, is

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Answer:

Correct Answer: 9. (2.0)

Solution:

  1. A=ai^ and B=acosωi^+asinωj^

A+B=(a+acosωt)i^+asinωtj^AB=(aacosωt)i^+asinωtj^|A+B|=3|AB|(a+acosωt)2+(asinωt)2=3(aacosωt)2+(asinωt)22cosωt2=±3×2sinωt2tanωt2=±13

ωt2=nπ±π6π12t=nπ±π6t=(12n±2)s=2s,10s,14s and so on. 



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