## Course Description

### Overview

This course is targeted at Singapore Cambridge GCE O level students, but is also relevant to IGCSE students and Singapore's Integrated program students.

Isaac Newton.

He's a big name in physics, with an equally big hairdo. You probably know him as the guy who got hit by an apple. He may seem like an old and outdated figure, but without his contributions to physics many of the things we take for granted now would not be possible (and that story about the apple is pretty fun!) This course, which investigates how forces make things move, is built heavily on the laws of motion that Newton laid down - the same laws which explain why you can make rockets fly upwards by pushing downwards, or why you seem to weigh more in an elevator accelerating upwards.

### Course Content

You will learn:

• Newton's 3 laws and how they work
• How to figure out what direction an object is going to go in when multiple forces are exerted on it
• How to figure out how fast that object's going to go
• How friction and air resistance will affect its motion

You will also learn:

• How to mess with the weight of an object
• Why all objects fall at the same speed (let's say you dropped a squirrel and an echidna off the leaning tower of Pisa...)
• Other cool stuff! (Some of the videos in this course are marked as "explanation videos", which go into greater depth on the topics covered. We try to bring in out-of-syllabus concepts where possible to make things more interesting and give a more complete understanding of the topic)

A link to the full O level Physics syllabus can be found here

### Course Prerequisites

You will need to know:

• How to watch videos on your computer Math Arena

The instructor is from Math Arena.The instructor is absolutely passionate about teaching and you'll find the lessons engaging and ultimately rewarding.

## Course curriculum

• 1

### Introduction

• Subject Content Requirements

• Q1 Which property of a solid object cannot be changed by the application of a force?

• 2

### Combining forces

• Q2 Which is the correct statement about force and velocity?

• Q3 Which object has the largest resultant force?

• Q4 Four forces act at a point as shown. What is the size of the resultant force?

• Q5 Forces X and Y act on a block in the directions shown on the scale diagram. In which direction is the resultant force acting?

• Q6 Two forces F1 and F2 act on an object O in the directions shown. What is the direction of the resultant force?

• Q7 Forces of 3N and 4N are acting as shown in the diagram. Which diagram may be used to find the resultant R of these two forces?

• Q8 Four forces act on a body X as shown below. Which of the following gives the approximate direction of the additional force required to keep the object in equilibrium?

• 3

### Solving problems with free-body diagrams

• Q9 A cupboard is attached to a wall by a screw. Which force diagram shows the cupboard in equilibrium, with the weight W of the cupboard, the force S that the screw exerts on the cupboard and the force R that the wall exerts on the cupboard?

• Q9 explanation

• Q10 Two blocks, one made of wood and the other of iron, are arranged at rest on the ground as depicted in combination I and II below. Which statement is correct?

• Q11 A pole of weight W is attached to a wall. It is held horizontal by a wire attached at point X of the pole. Which triangle of forces could correctly represent the three forces acting on the pole?

• Q12 A ladder ST, is on the point of slipping. Which one of the following diagrams correctly shows the directions of these forces?

• Q13 A weight W hanging from a string is pulled aside by a horizontal force P as shown in the diagram. The tension in the string is T. An increase in θ shows that

• 4

### Newton's Laws - Comparisons and observations using the 1st and 2nd laws

• Q14 A wooden block is pushed across a table at constant speed. Which statement is correct?

• Q15 An aircraft, flying at a constant height, is gaining speed. The four forces acting are Lift, Air resistance, Thrust and Weight. What is correct?

• Q16 An airship is moving forwards at constant height. Which statement is correct?

• Q17 In which situation is the resultant force on the body equal to zero?

• Q18 Five blocks of equal masses V, W, X, Y and Z are connected by four identical strings as shown in the diagram. They are pulled by a steadily increasing force F. Which of the strings A, B, C or D is most likely to break first?

• Q19 Which of the following graphs show(s) that a constant resultant force is acting on the object?

• 5

### Newton's Laws - Calculations using the 1st and 2nd laws

• Q20 A man pulls a sledge of mass 25kg across level ground with a horizontal force of 60N. A constant force of friction of 20N acts on the sledge. What is the acceleration of the sledge?

• Q21 A hard stone hits the ground and comes to rest almost immediately. As the stone hits the ground, what is the direction and the size of the force acting on the ground?

• Q22 A car of mass 1500 kg is towing a trailer of mass 1100 kg along a level road. The acceleration of the car is 1.30m/ s2 . Ignoring friction and air resistance, what is the driving force on the car?

• Q23 A person just supports a mass of 20 kg suspended from a rope. What is the resultant force acting on the mass?

• Q24 A car travelling at 30 ms-1 has to brake suddenly to avoid an accident. If the man inside weighs 80 kg and it takes 3 s to stop completely, what is the average force exerted by the man on his safety belt?

• Q25 When a block of wood of mass 2 kg was pushed along the horizontal flat surface of a bench, the friction force measured was 4 N. When the block was pushed along the same bench with a force of 10 N, it moved with a constant

• Q26 A boy of mass 40 kg jumps from rest from a platform of height 3 m. He lands by bending his knees and stops his body in 0.5 s after landing. What is the force exerted by his legs?

• 6

### Newton's Laws - Finally, the 3rd law

• Q27 The propeller on a boat pushes water backwards with a force of 2000N. The boat moves through the water against a total resistive force of 1800N. According to Newton’s third law, what is the forward force on the propeller due to the water?

• Q28 If you are launching a matchstick rocket, the action force is the rocket pushing the gases down. What is the reaction force?

• Q29 Two boys wearing in-line skates are standing on a smooth surface with the palms of their hands touching. If Boy X pushes by straightening his arms out while Boy Y holds his arms in the original position, what is the motion of the two boys?

• 7

### Mass and weight

• Q30 The inertia of a body is its resistance to changes in motion. Which property is a measure of the body’s inertia?

• Q31 On the Earth, the gravitational field strength is 10 N/kg. On the Moon, the gravitational field strength is 1.6 N/kg. If an object has a weight of 50 N on Earth, what is its weight on the Moon?

• Q31 explanation

• Q32 Which relationship defines gravitational field strength?

• Q33 A passenger is sitting in an aeroplane, which takes off and climbs to 10 000m. During this time, what happens to the mass and to the weight of the passenger?

• Q34 At a point on the surface of the Earth, the gravitational field strength is 9.8N/ kg. Which pair of values for mass and weight are correct for an object placed at this point?

• Q35 An object that has a mass of 15kg on the Earth is taken to the Moon. The gravitational field strength on the Earth is 10N/ kg and on the Moon is 1.6N/ kg. What are the mass and the weight of the object on the Moon?

• 8

### Mass and weight - Apparent weight in a moving elevator

• Q36 Your weight is 400N. You are standing on a weighing balance in an elevator. When the elevator just begins to move down the balance will read

• Q37 Your weight is 400N. When the elevator just begins to slow down while moving downward the balance will read

• Q38 Your weight is 400N. You are standing on a weighing balance in an elevator. When the elevator moves downward at constant velocity, the balance will read

• 9

### Freefall

• Q39 Two men jump out of an aeroplane at the same time. One of the men opens his parachute and the other man remains in free-fall. Why is the man in free-fall moving faster than the parachutist?

• Q40 A steel ball is released just below the surface of thick oil in a cylinder. During the first few centimetres of travel, what is the acceleration of the ball?

• Q41 An object X of mass m is released from a height h. Another object Y of mass 4m is released from a height 4h simultaneously. If both objects fall freely, which statement is true (ignoring air resistance)?

• Q41 explanation

• Q42 A ball bearing is released and sinks into liquid. It falls vertically until it reaches terminal velocity. In this duration, the resultant force on the ball bearing is

• Q43 An experiment is carried out by an astronaut on the surface of the Moon. A coin and a feather are dropped at the same instant from the same height. Which statement is correct?

• Q44 Two objects X and Y are identical in size and shape but X has 3 times the mass of Y. They are released from the same height in an evacuated chamber. Which one of the following statements is NOT correct?

• Q45 A ball was dropped from the window of an apartment located at the tenth story of a high rise building. 1 second after release, the ball was observed to have fallen by exactly 2 storeys. At which storey will the ball be 2 seconds after it was released?

• Q46 A student drops a table-tennis ball in air. What happens to the velocity and to the acceleration of the ball during the first few seconds after release?

• 10

### Special forces - Friction and the normal contact force

• Q47 In which example does friction act in the direction of forward motion of the object on which it acts?

• Q48 A body slides down a frictionless slope as shown. As the body presses on the surface, the surface pushes back on the body. The force of the surface on the body is sometimes called the reaction force. In which direction does the reaction force act?

• Q49 In which of the following is a force of friction necessary?

• 11

### Structured Questions

• SQ1 Block pulled on fricional surface

• SQ2 Car on road

• SQ3 Hot air balloon

• SQ4 Car being towed

• SQ5 (part 1) Ship-to-ship cable free body diagram

• SQ5 (part 1) explanation

• SQ5 (part 2) Ship-to-ship cable breaking cable

• SQ6 Tugboats