Here are we provide some most important extra questions and answers for class 9 science chapter wise For PT 3. If you read this questions then you will easily achieve more than 85% of marks in PT3.
Q 1. Explain Low of conservation of energy?
A. Energy neither be created nor be destroyed, it can change only one form to another form. Energy is constant before and after conservation.
Example:
Energy can neither be created nor destroyed, but it
is transformed from one form to another. Alternatively,
whenever energy gets transformed, the total energy
remains unchanged.
Proof – In case of a freely falling body
It may be shown that in the absence of external frictional force the total mechanical energy of a body remains constant.
Let a body of mass m falls from a point A, which is at a height h from the ground as shown in fig.
At A,
Kinetic energy kE = 0
Potential energy Ep = mgh
Total energy E = Ep + Ek = mgh + 0= mgh
During the fall, the body is at a position B. The body has moved a distance x from A.At B,velocity v2 = u2 + 2asapplying, v2 = 0 + 2ax = 2axKinetic energy Ek = 1/2 mv2 = 1/2 m x 2gx = mgx
Potential energy Ep = mg (h – x)
Total energy E = Ep + Ek = mg (h-x) + mgx = mgh – mgx + mgx= mgh
If the body reaches the position C.
At C,
Potential energy Ep = 0
Velocity of the body C is
v2 = u2 + 2as
u = 0, a = g, s = h
applying v2 = 0 + 2gh = 2gh
kinetic energy Ek =1/2 mv2=1/2 m x 2gh= mgh
Total energy at C
E = Ep + Ek
E = 0 + mgh
E = mgh
Thus we have seen that sum of potential and kinetic energy of freely falling body at all points remains same. Under the force of gravity, the mechanical energy of a body remains constant.
Q2. Define 1 jule?
A. When 1 N (Newton) force exerts on an object and it displace at distance 1 m.
Q3. Define 1 watt?
A. 1 watt is set to be when 1 joule work is done in 1 second.
Q4. Define wave length/ What is wave length?
A. The distance between two successive compression and rarefaction is known as wavelength.
Q5. What is Time period?
A. Time taken by wave for completing one oscillation is called time period.
Q5. What is Frequency?
A. The number of oscillation in per unit time (1 sec.) is called frequency.
Q6. What is Amplitude?
A. The maximum displacement of vibrating particles from it's mean position.
Q7. Range of hearing?
A. 20Hz - 20000Hz.
Q8. Properties of sound?
A. 1) Wavelength
2) Amplitude
3) Frequency.
Q9. Application of Archimedes Principal?
A. 1) Designing of ships and submarines
2) Hydrometer (Use for checking density of liquid)
3) Lactometer.
Q10. Carbon cycle explain with labeled diagram?
A.
Explanation :-
1) Carbon in atmosphere/water.
2) Plants take carbon dioxide.
3) Animal eat plants.
4) Through respiration Plants and animals release carbon dioxide in atmosphere.
5) Dead and decay animals/Plants convert into fossil fuels.
6) By combustion of fossil fuels Carbon dioxide release into atmosphere.
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