# Important Questions for Class 9 Chapter 10 - Gravitation

Important questions based on NCERT syllabus for Chapter 10 - Gravitation:

Question-1: Define pressure. Why is it difficult to hold a school bag having a strap made of a thin and strong string?

Solution: 1. Pressure is an expression of force exerted on a surface per unit area.
2. It is difficult to hold a school bag having a thin strap because the pressure on the shoulders is quite large. This is because the pressure is inversely proportional to the surface area on which the force acts. The smaller is the surface area; the larger will be the pressure on the surface. In the case of a thin strap, the contact surface area is very small. Hence, the pressure exerted on the shoulder is very large.

Question-2: You have a bag of cotton and an iron bar, each indicating a mass of 100 kg when measured on a weighing machine. In reality, one is heavier than other. Can you say which one is heavier and why? Define mass. Is it scalar or vector quantity?

Solution: 1. The cotton bag is heavier than the iron bar. The cotton bag experiences larger up thrust of air than the iron bar. So, the weighing machine indicates a smaller mass for cotton bag than its actual mass.
2. The mass of a body is the quantity of matter contained in it.
3. It is a scalar quantity.

Question-3: List out the physical quantities on which the gravitational force between objects depends.

Solution: The gravitational force between two objects depends on
a) the mass and
b) the distance between them