Question

A car is moving along a road with a speed of $45km/hr$. In what direction must a body be projected from it with a velocity of $25m/s$, so that its resultant motion is at right angles to the direction of car?

• A. At an angle of $120^{\circ }$ with the direction of motion of car.
• B. At an angle of $60^{\circ }$ with the direction of motion of car.
• C. At an angle of $90^{\circ }$ with the direction of motion of car.
• D. At an angle of $135^{\circ }$ with the direction of motion of car.

Answer 1

Answer: (A)

$v_c=45Km/h=\frac{25}{2}m/s$

For the resultant motion to be upwards.

$vcos\theta +v_c=0$

$cos\theta =\frac{v_c}{v}=-\frac{25/2}{25}=\frac{1}{2}$
$\Rightarrow \theta =120^{\circ }$