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SS1: PHYSICS – 1ST TERM

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  1. Introduction to Physics | Week 1
    4Topics
    |
    1 Quiz
  2. Measurement | Week 2
    3Topics
  3. Measurement of Mass | Week 3
    6Topics
    |
    1 Quiz
  4. Motion | Week 4
    5Topics
    |
    1 Quiz
  5. Velocity-Time Graph | Week 5
    4Topics
    |
    1 Quiz
  6. Causes of Motion | Week 6
    5Topics
    |
    1 Quiz
  7. Work, Energy & Power | Week 7
    3Topics
  8. Energy Transformation / Power | Week 8
    3Topics
    |
    1 Quiz
  9. Heat Energy | Week 9
    5Topics
    |
    1 Quiz
  10. Linear Expansion | Week 10
    6Topics
    |
    1 Quiz
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Power is defined as time rate of doing work. It is measured in Watt or Js-1.

Power =  \( \frac {work-done}{time} \scriptsize = \normalsize \frac {j}{s} \)

Power = \( \frac {force \: \times \: distance}{time}\scriptsize = \normalsize \frac {j}{s} \)  

P \( \scriptsize = Force \: \times \: \normalsize \frac {distance}{time}\)  

Velocity = \( \frac {distance}{time}\)

P = Force x Velocity

  = FV (Nms-1)

From the deduction, power can also be calculated by Force x Velocity.

Units of Power:

  • Watt
  • Joule per second J/s
  • Newton meter per second Nm/s
  • Kilogram meter per the second cube Kgm/s³

Example

i. A boy lifts a mass of 50kg vertically through a height of 3m in 20seconds. Calculate the power developed.

Solution

Values given:

mass = 50kg, height = 3m

t = 20 seconds

Power =  \( \frac {work-done}{time} \)

But work done = mgh = 50 x 10 x 3

=  \( \frac {50 \: \times \: 10 \: \times \: 3}{20} \)

=  \( \frac {1500}{20} \)

= 75 Watt

ii.  A force of 30N acts on a 0.5kg mass for 2 minutes. If the distance moved by the mass is 400cm,

calculate

(a) the power generated by the force.

(b) the acceleration of the object.

(c) its velocity.

Solution

Values Given:

Mass = 0.5kg, force = 30N

time = 2 minutes = 2 x 60 seconds = 120 seconds

distance = 400 cm = 400 / 100 = 4 m

(a) Power = \( \frac {work-done}{time} \)

Power = \( \frac {force \: \times \: distance}{time}\)  

Power = \( \frac {30N \: \times \: 4m}{120}\)  

Power = \( \frac {120}{120}\)

Power = 1 Watt

(b) To calculate the acceleration of the object, you use the formula,

Force = mass x acceleration.    

30 = 0.5 x acceleration.

Make acceleration the subject of the formula

acceleration = \( \frac {30}{0.5} \)

∴ acceleration = 60ms-2

(c) To calculate the velocity

use the formula

Power = force x velocity

velocity = \( \frac{Power}{force} = \frac{1}{30} \\ = \scriptsize 0.033 m/s \)

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