General Science 7th Class Chapter 8 Force and Motion Solved Exercise

General Science

7th Class

Chapter 8

Force and Motion

Questions

8.1 Encircle the correct option.

1. An example of contact force:

a. electrostatic force        b. muscular force

c. magnetic force        d. gravity

2. The force between two negatively charged particles is:

a. gravitational        b. frictional        c. repulsion        d. attraction

3. Which statement is true?

a. for every action force, there is a smaller reaction force in the opposite direction

b. for every action force, there is a smaller reaction force in the same direction

c. for every action force. there is an equivalent reaction force in opposite direction

d. for every action force, there is an equivalent reaction force in the same direction

4. The Earth's pull on the objects is called:

a. gravity        b. frictional force        c. electrostatic force        d. magnetic force

5. A batsman hits the ball back towards the bowler, which effect of force is seen:

a. change of shape        b. change of direction

c. change of state from motion to rest        d. change of state from rest to motion

6. Which one of the following statements is correct?

a. 1m = 1000 km        b. m/s is the unit of displacement

c. N is the unit of force        d. 1hr = 60s

7. Which one of the following statements is not correct?

a. Displacement is the shortest distance between two points

b. Displacement is the distance covered in one second

c. Meter (m) is the unit of displacement

d. Rate of change of distance with time is called speed

8.2 Define the following:

1. Contact forces

2. Non-contact forces

3. Gravitational force

4. Displacement

5. Speed

1. Contact forces

Ans.

Contact forces are those forces that act only when objects are in physical contact with other objects and bring about necessary changes.

Examples: muscular force, frictional force

2. Non-contact forces

Ans.

Some forces do not involve physical contact between the objects on which they act. They act through the space between them. Such forces are called non-contact forces.

Examples: Magnetic force, electrostatic force and gravitational force.

3. Gravitational force

Ans.

The force due to which every body of the universe attracts every other body is called force of gravitation.

4. Displacement

Ans.

Displacement is defined as the shortest distance between two points.

5. Speed

Ans.

Speed is defined as the distance travelled per unit time.

Speed = Distance / time