Simple Harmonic Motion 5 Question 5

10. A point mass is subjected to two simultaneous sinusoidal displacements in x-direction, x1(t)=Asinωt and

x2(t)=Asinωt+2π3. Adding a third sinusoidal displacement x3(t)=Bsin(ωt+φ) brings the mass to a complete rest. The values of B and φ are

(2011)

(a) 2A,3π4

(b) A,4π3

(c) 3A,5π6

(d) A,π3

Show Answer

Answer:

Correct Answer: 10. (b)

Solution:

Resultant amplitude of x1 and x2 is A at angle π3 from A1. To make resultant of x1,x2 and x3 to be zero. A3 should be equal to A at angle φ=4π3 as shown in figure.

Correct answer is (b).

Alternate Solution.

It we substitute, x1+x2+x3=0

or Asinωt+Asinωt+2π3+Bsin(ωt+φ)=0

Then by applying simple mathematics we can prove that

B=A and φ=4π3



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