Final answer:
A man's weight will slightly increase when traveling from a hilly region to the Terai due to the stronger gravitational force at a lower altitude.
Step-by-step explanation:
When a man travels from a hilly region (higher altitude) to the Terai region (lower altitude), there will be a slight increase in his weight. This is due to the fact that gravitational force is stronger at lower altitudes, where the distance to the center of the Earth is less. The force of gravity is proportional to the mass of two objects and inversely proportional to the square of the distance between their centers. Thus, as one moves from higher to lower altitudes, the distance to the Earth's center decreases, and the gravitational force slightly increases, which means a person will weigh more at lower altitudes.
For example, consider a hiker of mass 70 kg at different altitudes. As the hiker descends from the top of a mountain to sea level, they will experience a slight increase in weight due to the stronger gravitational pull. This phenomenon illustrates that air density and altitude have a relationship similar to weight and altitude, where air density decreases as altitude increases, leading to thinner air at higher elevations such as Mount Everest.
This concept is also demonstrated by the sensation of weight change in a high-speed moving elevator. Your weight seems to decrease when the elevator rapidly accelerates downwards and increase when it moves upwards, which can be noticed and measured on a scale within the elevator.