1.

Two forces of equal magnitude F act at a point. If the angle between them is θ, then the magnitude of the resultant force is

Answer»

`F sqrt(2(l-sintheta))`
`Fsqrt(2(l+sintheta))`
`2Fsin(theta)/2`
`2Fcos(theta)/2`

SOLUTION :Magnitude of RESULTANT of two force
`R=sqrt(F_(1)^(2)+F_(2)^(2)+2F_(1)^(2)F_(2)^(2)costheta)``F_(1)^(2)=F_(2)^(2)=F`
implies`R = sqrt(F^(2)+F^(2)+2F^(2)costheta)`
implies `R = sqrt(2F^(2)+2F^(2)costheta)`
`implies R = sqrt(2F^(2)(1 +costheta)`
since, `1+costheta = 2 cos^(2)theta/2`
`R = sqrt(2F^(2)(2cos^(2)theta/2))`
`R = sqrt(4F^(2)cos^(theta/2))`
`R = 2Fcostheta/2`.


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