Question

(a) If a balloon filled with air and its mouth untied, is released with its mouth in the downward direction, it moves upwards. Why?
(b) An unloaded truck weighing 2000 kg has a maximum acceleration of 0.5 m/s². What is the maximum acceleration when it is carrying a load of 2000 kg?

Answer 1

(a) If the inflated balloon is released with its mouth untied in the downward direction, then it will move upwards because the air rushes out of balloon in the downward direction. The equal and opposite reaction of downward thrust of air pushes the balloon upwards.

(b) Force of unloaded truck:
m = 2000 kg
a = 0.5 m/s²
Force = mass × acceleration
= 0.5 × 2000
= 1000 N
Force of loaded truck:
We have to find maximum acceleration,
M = [2000+2000]
Force = mass × acceleration
⇒ 1000 = a × 4000
$$\begin{gathered} \Rightarrow \frac{1000}{4000}=a \\ \Rightarrow a=0.25 \end{gathered}$$
The maximum acceleration when it is carrying a load of 2000 kg is 0.25 m/s².