Question

If a body is thrown with a velocity of $19.6m/s$ making an angle of ${30}^o$ with the horizontal, then the time of flight is

• A. $1s$
• B. $2s$
• C. $2\sqrt{3}s$
• D. $5s$

Answer 1

The correct option is B $2s$

$\text{Step 1: Draw the projectile [Refer Fig.]}$

Component of velocity in x and y direction :

$u_x=u\cos \theta ;u_y=u\sin \theta$

$\text{Step 2: Time of flight calculation}$

Since acceleration is constant, therefore applying equation of motion in $y$ direction (Taking upward positive)

$s_y=0u_y=u\sin {30}^o{a}_y=9.80m/s^2$

$s_y=u_{y}t+\frac{1}{2}{a}_y{t}^2$

$\Rightarrow$ $0=19.6\sin {30}^{o}t-\frac{1}{2}\times 9.80t^2$

$\Rightarrow$ $t=2s$

Hence option $B$ is correct.