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Motion In Straight Line

Question
CBSEENPH11017130

Two straight lines drawn on the same displacement time graph make angle 30° with each other as shown in the figure. For what value of straight theta velocity of A will be three times the velocity of B?


Solution
On analysing the given graph,
Velocity of the particle A is given by, 
straight v subscript straight A space equals space tan space left parenthesis straight theta plus 30 to the power of straight o right parenthesis space 
Velocity of particle B is given by, 
straight v subscript straight B space equals space tanθ 
Here, v= 3 vB 
tan space left parenthesis theta space plus space 30 to the power of o right parenthesis space equals space 3 space tan space theta
U sin g space t h e space f o r m u l a space o f space tan space left parenthesis A plus B right parenthesis comma space w e space h a v e

space space space space fraction numerator tan space theta space plus space space tan space 30 to the power of 0 over denominator 1 space minus tan theta space tan space 30 to the power of o end fraction space equals space 3 space tan space theta

rightwards double arrow space space tan theta space plus space tan 30 to the power of 0 space equals space 3 space tan theta space minus space 3 space tan squared theta space tan space 30 to the power of o space

rightwards double arrow space space 3 space tan space 30 to the power of o space tan squared theta space minus space 2 space tan theta space plus space tan space 30 to the power of o space equals space 0 space

rightwards double arrow space space space space space tan space theta space equals space fraction numerator 2 plus-or-minus square root of 4 space minus 12 space tan squared 30 to the power of o end root over denominator 6 space tan space 30 to the power of o end fraction

S u b s t i t u t i n g space tan space 30 to the power of o space equals space fraction numerator 1 over denominator square root of 3 end fraction comma space w e space g e t
space space space space space space space space tan space theta space equals space fraction numerator 1 over denominator square root of 3 end fraction space

rightwards double arrow space space space space space space space space space space space space theta space equals space 30 to the power of o