First slide
Vectors
Question

The resultant of two forces cannot exceed

Moderate
Solution

If α be the angle between the forces P

and  Q, then their resultant is given by R

\large \[\sqrt {{P^2} + {Q^2} + 2PQ\cos \alpha } = \sqrt {{P^2} + {Q^2} + 2PQ - 2PQ + 2PQ\cos \alpha } \]

⇒R =

\large \sqrt {{{(P + Q)}^2} - 2PQ(1 - \cos \alpha )}

Since (1+cosα) is positive , magnitude of resultant R is less than or equal to 

\large \sqrt {{{(P + Q)}^2}}

i.e R ≤ (P+Q), equality sign holds good when (1-cosα) = 0 i.e α =00.

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