Question

A balloon lifting in air follows:
A. Law of gravitation
B. Archimedes’ principle
C. Laws of motion
D. All of the above

Answer 1

Recall the statements of the law of gravitation. Archimedes’ principle and law of gravitation. Check the forces acting on the balloon lifting upward in the air. Relates the concepts used in all these laws with the forces acting on the balloon and motion of the balloon and checks which of the laws is satisfied by the balloon lifting in air.

Complete answer:
We have asked to check the balloon lifting in air follows which of the laws given in the options.When the balloon is lifting upwards, the gravitational force of attraction of the Earth acts on the balloon and the weight of the balloon always acts in the downward direction.This shows that the balloon lifting in air follows the law of gravitation.

When the balloon is lifting in the air the upward thrust or buoyant force acts on the balloon. Since this buoyant force is greater than the weight of the balloon, the balloon continues to move upward.This shows that the balloon lifting in air follows Archimedes’ principle.

The balloon is moving in the air in the upward direction. The buoyant force exerted by the air is causing the balloon to move upward. (Newton’s first law of motion).The net force acting on the balloon is given by the mass of the balloon and acceleration of the balloon. (Newton’s second law of motion)
$\rho Vg - mg = ma$

The buoyant force acting on the balloon is equal to the weight and force due to acceleration of the balloon. (Newton’s third law of motion)
$\therefore\rho Vg = ma + mg$
This shows that the balloon lifting in the air follows the law of motion.Therefore, the balloon lifting in the air follows the law of gravitation, Archimedes’ principle and laws of motion.

Hence, the correct option is D.

Note: The students may assume that the balloon is lifting upward in the air medium and for the balloon to follow Archimedes’ principle, there must be a liquid medium. So the balloon cannot follow Archimedes’ principle. But the students should keep in mind that according to Archimedes’ principle there must be a fluid which can be liquid or gas.