Question

A hot air balloon is rising with an acceleration of 10 $m/s^2$. The moment when its velocity is 10 m/s, a stone is dropped which of the following is the displacement time graph of the stone with respect to the balloon.

• A.
• B.
• C.
• D.

Answer 1

The correct option is B

Okay so what we know when stone is dropped :
$u_{balloon}=+10m/s$
$a_{balloon}=+10m/s^2$
$u_{stone}=+10m/s$ by now, think you know why velocity of stone is velocity of balloon
$a_{stone}=-10m/s^2$
To find $s_{s/b}$
$s=ut+\frac{1}{2}a{t}^2$
$u_{s/b}=10-10=0$
$a_{s/b}=-10-10=-20m/s^2$
$s_{s/b}=-10t^2$

Now, Draw s on y - axis
f on x-axis
How will it look?
y = -10$x^2$
Well if you don't then no problem. Be smart. Substitute some valves and draw the graph and see.

So the graph should look like this.