Question

A car is moving along a road with a speed of $45 \,km/hr$. In what direction must a body be projected from it with a velocity of $25 \,m/s$, 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)

$v_{c}=45\, Km/h =\frac{25}{2} \,m/s$
For the resultant motion to be upwards.
$v\,\,cos\,\, \theta+v_{c}=0$
$cos\,\,\theta=\frac{v_c}{v} = -\frac{25/2}{25} =\frac{1}{2}$
$ \Rightarrow \theta =120^{\circ}$