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CodeVID-P9-02-CH-01
Force and Laws of Motion — Chapter 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 where asked and show full working with correct SI units in numerical answers.
Section A — Multiple Choice Questions
6 × 1 = 6 marks
1.
The SI unit of force is the:
- A.joule
- B.newton
- C.watt
- D.pascal
2.
Mass of a body is a measure of its:
- A.weight
- B.inertia
- C.momentum
- D.speed
3.
Momentum is given by:
- A.$mv$
- B.$ma$
- C.$m/v$
- D.$v/m$
4.
One newton equals:
- A.$1\ \text{kg m/s}$
- B.$1\ \text{kg m/s}^2$
- C.$1\ \text{kg/s}$
- D.$1\ \text{N m}$
5.
Action and reaction forces act on:
- A.the same body
- B.two different bodies
- C.no body
- D.the ground only
6.
The recoil of a gun illustrates conservation of:
- A.energy
- B.momentum
- C.mass
- D.force
Section B — Short Answer (2 marks)
4 × 2 = 8 marks
7.
Define inertia and state how it depends on mass.
8.
Find the momentum of a $6\ \text{kg}$ body moving at $5\ \text{m/s}$.
9.
State Newton's Third Law of Motion.
10.
A $4\ \text{N}$ force acts on a $2\ \text{kg}$ body. Find its acceleration.
Section C — Short Answer (3 marks)
2 × 3 = 6 marks
11.
A $1200\ \text{kg}$ car accelerates from rest to $18\ \text{m/s}$ in $6\ \text{s}$. Find the force.
12.
Explain, using $F = \Delta p/\Delta t$, why airbags reduce injury in a car crash.
Section D — Long Answer (5 marks)
2 × 5 = 10 marks
13.
State the law of conservation of momentum. A gun of mass $3\ \text{kg}$ fires a $0.03\ \text{kg}$ bullet at $200\ \text{m/s}$. Find the recoil velocity of the gun and explain why it is small.
14.
Define momentum and Newton's Second Law. A $2\ \text{kg}$ object moving at $5\ \text{m/s}$ collides with and sticks to a stationary $3\ \text{kg}$ object. Find their common velocity and the change in momentum of the $2\ \text{kg}$ object.
Answer Key
Section A — Multiple Choice Questions
- (B) newton
- (B) inertia
- (A) $mv$
- (B) $1\ \text{kg m/s}^2$
- (B) two different bodies
- (B) momentum
Section B — Short Answer (2 marks)
- Inertia is the tendency to resist a change in the state of motion; greater mass means greater inertia.
- $p = mv = 6 \times 5 = 30\ \text{kg m/s}$.
- To every action there is an equal and opposite reaction, acting on two different bodies.
- $a = F/m = 4/2 = 2\ \text{m/s}^2$.
Section C — Short Answer (3 marks)
- $a = 18/6 = 3\ \text{m/s}^2$; $F = ma = 1200 \times 3 = 3600\ \text{N}$.
- Airbags increase the stopping time $\Delta t$, so for the same $\Delta p$ the force on the passenger is reduced.
Section D — Long Answer (5 marks)
- Conservation: total momentum stays constant with no external force. $v_g = m_b v_b/m_g = (0.03 \times 200)/3 = 6/3 = 2\ \text{m/s}$ backward. It is small because the gun's mass is much larger than the bullet's, so it needs only a small velocity for equal momentum.
- Momentum $p = mv$; Second Law: $F = \Delta p/\Delta t$. Common velocity: $2 \times 5 = (2+3)v \Rightarrow v = 10/5 = 2\ \text{m/s}$. Change in momentum of $2\ \text{kg}$ object $= 2(2 - 5) = -6\ \text{kg m/s}$.
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