Vidaara.orgClass 9 · Physics
CodeVID-P9-02-FIN-01
Balanced & Unbalanced Forces; Inertia — Assignment
Name: ____________________
Roll No.: __________
Date: ____________
General Instructions
- All questions are compulsory.
- Section A carries 1 mark each, Section B 2 marks, Section C 3 marks and Section D 5 marks.
- Draw neat labelled diagrams wherever required and show full working in numerical answers.
Section A — Multiple Choice Questions
5 × 1 = 5 marks
1.
The SI unit of force is the:
- A.joule
- B.newton
- C.watt
- D.pascal
2.
Balanced forces acting on a body produce a net force of:
- A.maximum
- B.zero
- C.infinite
- D.negative
3.
Inertia of a body depends on its:
- A.speed
- B.mass
- C.shape
- D.colour
4.
An unbalanced force on a body always produces:
- A.rest
- B.acceleration
- C.zero velocity
- D.no change
5.
Newton's First Law is also called the law of:
- A.gravitation
- B.inertia
- C.momentum
- D.action
Section B — Short Answer (2 marks)
4 × 2 = 8 marks
6.
Define balanced and unbalanced forces with one example each.
7.
State Newton's First Law of Motion.
8.
Why does dust fly off a carpet when it is beaten with a stick?
9.
Name the three types of inertia.
Section C — Short Answer (3 marks)
3 × 3 = 9 marks
10.
A force of $80\ \text{N}$ pushes a crate right while friction of $30\ \text{N}$ opposes it. Find the net force and its effect.
11.
Explain, using inertia, why it is dangerous to travel in an overloaded vehicle.
12.
With an example, explain inertia of direction.
Section D — Long Answer (5 marks)
1 × 5 = 5 marks
13.
Define inertia. Explain its three types with one everyday example of each, and state how mass is related to inertia.
Answer Key
Section A — Multiple Choice Questions
- (B) newton
- (B) zero
- (B) mass
- (B) acceleration
- (B) inertia
Section B — Short Answer (2 marks)
- Balanced: net force zero, e.g. a book on a table; unbalanced: net force non-zero, e.g. a kicked ball.
- A body stays at rest or in uniform straight-line motion unless acted on by an unbalanced force.
- The carpet moves but dust, by inertia of rest, stays put and so separates from it.
- Inertia of rest, inertia of motion and inertia of direction.
Section C — Short Answer (3 marks)
- Net force $= 80 - 30 = 50\ \text{N}$ to the right; the crate accelerates right.
- Greater mass means greater inertia, so the vehicle is harder to stop, increasing braking distance and accident risk.
- A body resists changing its direction; mud flies off tangentially from a rotating cycle wheel.
Section D — Long Answer (5 marks)
- Inertia is resistance to change in state of motion. Rest: coin drops into glass when card is flicked; motion: passenger lurches forward on braking; direction: mud flies off a wheel. Mass is the measure of inertia — more mass, more inertia.
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