A helium balloon is tied to the floor of a bus that is moving uniformly along a…
PHYSICS · Multi-part · CBSE · Physics · Laws of Motion · Laws of Motion
Problem
A helium balloon is tied to the floor of a bus that is moving uniformly along a straight road. The forces acting on the balloon are:
• Upward buoyant force of the air
• Downward weight of the balloon
• Small backward force of air drag because of a cross-wind entering from the front window
• Forward tension in the string holding the balloon to the floor
(i) Draw a labelled free-body diagram showing all the forces acting on the balloon while the bus is moving uniformly.
(ii) Explain whether the set of forces in the vertical direction are balanced or unbalanced. What consequence does this have for the vertical motion of the balloon?
(iii) Explain whether the set of forces in the horizontal direction are balanced or unbalanced while the bus is moving at constant speed. What is the horizontal motion of the balloon in this state?
(iv) The driver suddenly applies the brakes and the bus slows down quickly. Using Newton’s first law of motion, predict and justify qualitatively the immediate motion of the balloon just after the brakes are applied, considering both vertical and horizontal directions.