Worked Examples-Calculation Part 1 - Work, Energy and Power

Considered Formula;

$$\text {i)}\quad W.d = F \times d$$ $$\qquad \text {Where}~~W.d \to Work~done,\quad F \to Force \\\qquad d \to Distance~moved$$ $$\text {ii)}\quad K.E = \frac {1}{2}mv^2$$ $$\qquad \text {Where}~~K.E \to Kinetic~energy,\quad m \to Mass \\\qquad v \to Velocity$$

Example

Abu Nufayl lifts a sack of rice by a force of 250 N against gravity to 2 m high. Calculate his work done

Solution

Data given

Force (F) =250 N

Distance (d) = 2 m

Work done (W.d) =?

$$~~~~~~~~~~~~~~~~~~~~~~~~~~~~W.d = F \times d$$ $$~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ = 250 \times 2$$ $$~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ = 500~Joules$$

The work done by Abu Nufayl = 500 Joules     CONTINUE READING

Measurement of Temperature

Temperature is measured by thermometer on physical properties that change linearly with temperature to give temperature readings. Physical properties of a thermometer include;

i)        Expansion of liquid (mercury or alcohol) when heated

ii)       Expansion of a compound strip of two metals

iii)     Thermoelectric property change in which when junction of two different metals are heated an electric current is generated

iv)     Change of resistance of a wire e.g. platinum resistance thermometer

Thermometric Scales

There are two scales of thermometer include;

i)        Celsius or Centigrade Scale

ii)       Fahrenheit Scale

Celsius or Centigrade Scale

This scale has 100 divisions between the upper and lower standard points. This scale was introduced by   CONTINUE READING

Warning Signs

Warning sign is the symbol established to ensure safety in the laboratory and in other field like goods or commodities. This signs should have obeyed to avoid accidents, include Toxic, Harmful/Irritant, Flammable, Oxidizing agent, etc

Flammable

Flammable symbol means that the substance can catch fire easily. For Example, , gasoil, kerosene, petrol, butane, methane, spirit, nail polish remover, turpentine etc.

Toxic

Toxic symbol means that a substance is dangerous and can cause death within a short time. Toxic substances containing poisonous ingredients, Example, of toxic substance is jik, mercury etc. 

Oxidizing Agent

Oxidizing agent symbol means that the substance can speed up the rate of burning. For Example, oxygen gas, chlorine gas, fluorine gas and   CONTINUE READING

Mechanics - Simple pendulum - Experiment 5

The aim of this experiment is to find the ratio P defined in part (d) by using a simple pendulum.

Suspend the pendulum bob with its upper part of the string fixed on a retort clamp as shown in figure below. Make a knot Nat a distance of L =10cm from the bob B. While X is the distance between the point of suspension S to a knot N on the string

Set X=60cm and pull the bob aside at a small angle so that it can start swinging vertically

(a)  Record the time t for 30 oscillations of the pendulum bob

(b)  Repeat the above procedure for the values of X= 50, 40, .....  CONTINUE READING

Solution - Extra Explaining Questions - ELECTROMAGNETISM

ELECTROMAGNETISM

1. Explain why transformer are used to reduce the current passing through the transmission cables of the National Grid

[Show answer]

The transformer (Step –up) reduces the current passing through the transmission cables of the National Grid so as to reduce the energy wasted (Power Loss) by heating up the cables.

2.   Explain why transformer does not work using a d.c. supply. Why is an a.c. supply necessary to make a transformer work?

[Show answer]

According to Faraday Law of Electromagnetism that says “wherever there is change of magnetic flux (linking the coils) e.m.f is induced, so if the d.c is supplied to the primary coil of the transformer the magnetic field is constant (No change of magnetic flux). Then no potential difference (voltage) induced in the secondary coil.

3.  Explain why a bicycle lamp attached to the to the dynamo does not light when the.....  CONTINUE READING

FRICTION FORCE AT INCLINED PLANE

Consider the diagram below, a mass of body sliding down the incline plane

At constant speed a = 0m/s²

F_k = mgsinθ

R = mgcosθ

But:

Fk = μ_kR – make μ_k subject

μ_k = F_k/R

μ_k = mgsinθ/mgcosθ

μ_k = sinθ/cosθ

μ_k = Tanθ

Therefore, at constant speed coefficient of ..  CONTINUE READING

Cooling Effect of Evaporation

What is evaporation?

Evaporation is the gradual change of state from liquid to gas that occurs at the surface of the liquid

Evaporation occurs when particles escape from a liquid. This happen even when the temperature is lower than the boiling point.

Factors affecting evaporation

i.     Temperature

An increase of temperature increases the rate of evaporation

ii.    Surface area

A larger surface area allows more particles to leave the liquid hence the larger the surface area the higher rate of evaporation..  CONTINUE READING

Extra Explaining Questions - ELECTROMAGNETISM

ELECTROMAGNETISM

1. Explain why transformer are used to reduce the current passing through the transmission cables of the National Grid

2.   Explain why transformer does not work using a d.c. supply. Why is an a.c. supply necessary to make a transformer work?

3.  Explain why a bicycle lamp attached to the to the dynamo does not light when the bicycle is stationary?

4.   A student is trying to test a transformer using battery. Explain why the voltmeter connected to the secondary coil reads 0 V?

5.   A wire is made to move through a magnetic field so that a potential difference is induced across its ends. State two ways in which the...  CONTINUE READING

Screw Jack

A Screw Jack consist of a cylinder with a spiral ridge runs round it. The spiral is called the thread (T) and the distance between two adjacent threads is called the pitch (p) of the screw.
Consider the following diagram.

Example 1

 A screw jack with a pitch of 0.2cm and a handle of length 50cm is used to lift a car of weight 1.2 x 10⁴N. If the efficiency of the screw is 30%, find:

a)    The velocity ratio and mechanical Advantage of the machine.  CONTINUE READING

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Concept Of Simple Machines

Simple machine is any device, which requires single force in operation to simplify work e.g. Claw – hammer, a pulley, and an inclined plane.

In a simple machine, a force is applied at one convenient point to overcome another force acting at another point.

The diagram above shows a stone being shifted. Force is applied at one end of the bar in order to exert an upward force on the stone. The down ward force is called effort and the weight of the stone is called load.

Effort is the force used to operate a machine.

Load is the resistance, which machines overcome..  CONTINUE READING

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Extra Calculation Questions - Pressure

PRESSURE

Calculation questions in topic of pressure are now released for you to access and make you are own practices. Also you may access more questions found in other pages such those found in Exercises 

1.       What pressure does a diver experiences at a depth of 16 m in a diving tank? The density of water is 1,000 Kg/m³ and the atmospheric pressure is 100,000 Pa

2.       The figure below shows a simple type of   hydraulic braking system. The areas of cross section of the small cylinder and large cylinder are 0.0004 m² and 0.0024 m² respectively. A pedal is pushed against the piston in the small cylinder with a force of 90 N.

i)        Calculate the pressure exerted on the brake fluid.

ii)       Calculate the force exerted by the brake fluid on the piston of the large cylinder.
CONTINUE READING 

What is smoothing as used in Half-Wave rectifier?

WHAT IS RECTIFICATION?

Is the process which an alternating current is formed to only flow in one direction. Rectification is done by using of diodes.

OR

Rectification is the process of converting alternating current to pulsating direct current. CONTINUE READING

Do You Know X - Rays?

X – Rays are electromagnetic waves of high energy and very short wavelength produced when fast moving electrons strikes a metal target.

X – Rays are produced when fast moving electrons strike a metal target releasing their energy which is converted to X – rays.  CONTINUE READING

INTERFERENCE OF WAVES

Is the phenomena in which two waves superpose to form a resultant wave of greater or lower amplitude

OR

Is the phenomenon that occurs when two waves meet while travelling along the same medium.

PRINCIPLE OF SUPERPOSITION

The principle of superposition states that:-

²The resultant displacement at any point is equal to the sum of the displacements of different waves at the point’’  CONTINUE READING 

Work, Energy and Power Solving 1

Considered Formulas

Example 1

A man moves a stone by a force of 45 N to distance of 4 m long. What is the work done by the man?

Continue