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ICSE physics

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Question
ICSEENIPH10005781
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What is the SI unit of energy? How is the electron volt (eV) related to it? 

Solution

Joule (J) is the SI unit of energy. 

1 eV = 1.6 × 10-19 J 

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Question
ICSEENIPH10005782
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State the energy changes that takes place in the following when they are in use:

i) a photovoltaic cell

ii) an electromagnet

Solution

i) Light energy to electrical energy.

ii) Electrical energy to mechanical energy

Question
ICSEENIPH10005783
Wired Faculty App

A body of mass 5 kg is moving with a velocity of 10 m/s. What will be the ratio of its initial kinetic energy and final kinetic energy, if the mass of the body is doubled and its velocity is halved? 

Solution

K. E subscript 1 space equals space 1 half space m v squared space italic space italic space italic space italic space italic space italic space italic space italic space equals space 1 half space cross times space 5 space cross times space left parenthesis 10 right parenthesis squared space italic space italic space italic space italic space italic space italic space italic space italic space italic space equals 1 half cross times 500 space equals space 250 space J K. E subscript italic 2 space equals space italic 1 over italic 2 space m v to the power of italic 2 space italic space italic space italic space italic space italic space italic space italic space italic space equals space italic 1 over italic 2 space cross times space 10 space cross times space left parenthesis 5 italic right parenthesis to the power of italic 2 space italic space italic space italic space italic space italic space italic space italic space italic space equals space 5 space straight x space 25 space equals space 125 space straight J fraction numerator K. E subscript 1 over denominator K. E subscript 2 end fraction space equals space 250 over 125 space equals 2 over 1   
Initial kinetic energy will become twice of the final kinetic energy. 

Question
ICSEENIPH10005784
Wired Faculty App

6.5 kJ of energy causes a displacement of 64 m in a body in the direction of force in 2.5 seconds. Calculate:

i) the force applied

ii) power in horse power(hp)

[ Take 1 hp = 764 W]

Solution

Given:
E = 6.4 kJ = 6400 J
D = 64 m
T = 2.5 sec
i) Force space equals space Energy over Displacement space equals space 6400 over 64 space equals space 100 space straight N 
ii) Let,

Error converting from MathML to accessible text.

Question
ICSEENIPH10005785
Wired Faculty App

An object of mass 'M’ is allowed to fall freely from point A as shown in the figure. Calculate the total mechanical energy of the object at:

i) Point A

ii) Point B

iii) Point C

iv) State the law which is verified by your calculations in parts (i), (ii), and (iii).

Solution

i)
At point A:
Total Energy = K.E + P.E
                 = 0 + mgh

                 = mgh

                 = mg (x+y) 

ii)
At point B:
Total energy = K.E + P.E
Error converting from MathML to accessible text. 

iii)
At Point C:

Total Energy:

P.E + K.E 
= 0 + 1 half mv squared
Error converting from MathML to accessible text.
iv)
Law of conservation of energy.

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