Question

A projectile is thrown with a velocity of $50{\text{ms}}^{-1}$ at an angle of ${53}^{\circ }$ with the horizontal. Choose the incorrect statement

• A. It travels vertically with a velocity of $40{\text{ms}}^{-1}$ at all times
• B. It travels horizontally with a velocity of $30{\text{ms}}^{-1}$
• C. The minimum velocity of the projectile is $30{\text{ms}}^{-1}$
• D. The body has a constant acceleration in the downward direction

Answer 1

The correct option is A It travels vertically with a velocity of $40{\text{ms}}^{-1}$ at all times

$u_y=u\sin \theta$
$=50\sin {53}^{\circ }=50\times \frac{4}{5}$
$=40{\text{ms}}^{-1}$
We know, $v_y=u\sin \theta -gt$ (during upward journey) and $v_y=gt$ (during downward journey)
So, $v_y$ first decreases and then increases during the projectile motion.
Hence, option (a) is incorrect
$u_x=u\cos \theta$
$=50\times \frac{3}{5}=30{\text{ms}}^{-1}$
As the horizontal component remains constant. Thus, option (b) is correct
Velocity is minimum when its vertical component becomes $0$
$\Rightarrow u_{min}=u\cos \theta =30{\text{ms}}^{-1}$.
That is at the highest point.
Hence, option (c) is also correct.
The body has a constant acceleration$\left(g\right)$ in the downward direction.
Hence, option (d) is also correct.