Question

A projectile is thrown with velocity v making an angle o with the horizontal. It just crosses the top of two poles, each of height h, after 1 second and 3 second respectively. The time of flight of the projectile is (A) 1 S (B) 3 s (0) 4 s (D) 7.8

JEE/Engineering Exams

Physics

Solution

142

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vertical cossponent of velocing ( v_{4}=v sin theta ) ( N O_{0} O, quad u sin y quad S=u+1 frac{1}{2} a t^{2} ) here ( , y=u_{y} t+frac{1}{2} a y t^{2}left(because a_{y}=yright) ) ( o r, y=V sin theta t-frac{1}{2} g t^{2} ) After pusting ( t=1 ) sec then ( (y=11) ) ( h=v sin theta-frac{1}{2} g-r(hat{theta}) ) again ils we puf ( t=3 ) sec then ( y=h ) ( h=3 v sin theta-frac{9}{2} g r ) from (1) and ( widehat{C i} ) [ 2 v sin theta=4 g ] now, time of blight? ( T=frac{2 v sin theta}{j} ) [ 2 frac{9 g}{0}=4 sec ] oppion ( ()