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Physics: Post your doubts here!

DeadlYxDemon

DeadlYxDemon

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*AS LEVEL*
Please I need answers for the following QUESTIONS
1) Explain fundamental and derived units.
2) a) How would you check the homogeneity of a equation?
b) An obstacle of width a is placed in a fluid having a density ρ, and viscosity η. The streamline flow of th fluid becomes turbulent if the flow speed exceeds a critical value v. Which of the equations below relates v, a, ρ and η correctly?

i) v = Aηa/ρ ii) v = Bη/aρ iii) v = Cρa/η

3)
The pressure p is due to a liquid of density ρ is related to the depth h by the expression

p= ρgh

Where g is the acceleration of free fall. Use this expression to determine the derive units of pressure. Explain your working.
 
Last edited:
Thought blocker

Thought blocker

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Charlotte20102013 said:
No, you have only provided P12, while I need P11.
Click to expand...
If you not getting his solution, here is a paste link of it. :)
9 – Ans: B. Terminal velocity is reached when air resistance equals the force of gravity (this is constant since the mass of the body is constant). So, it depends on the mass of the body. Since the mass is related to density and volume (shape), the terminal velocity is affected by all three. Since the question says that the terminal velocity IS reached, the height is not relevant here.

10 – Ans: C. The force on a body is DEFINED as the rate of change of momentum of the body. This does equal to the product of mass and acceleration but for A-Level, this is NOT accepted as a DEFINITION.

30 – Ans: C. Interference pattern is only along XY (although there can be 1 along PQ, but this was not an option). Note that waves are produced at P and Q. Phase difference between waves from P and Q is constant along line RS (since waves are coherent and RS is midway from P and Q), so there can be no interference pattern along RS. From this, ans A, B and D are eliminated.

32 – Ans: C. Force = total EQ = E(+Q) + E(-Q) = 0. Electric field is from +ve to –ve. So, charge +Q will go downwards while charge –Q will go upwards (unlike charges attract) causing a resultant anti-clockwise torque.

33 – Ans: A. R = ρL/A. So, resistivity ρ = RA / L. The electrical resistivity of material is numerically equal to resistance in ohms of a cube of that material, cube being of side length 1 metre (since length is 1m, both A and L in above equation is 1. So, ρ = R) and resistance being measured between opposite faces.

Answer C is true only if the sample is a wire (consider a cuboid for example, it will have different cross-sectional area – it is known that for a material, the electrical resistivity is constant, independent of the shape of the sample)
 
Charlotte20102013

Charlotte20102013

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Thought blocker said:
If you not getting his solution, here is a paste link of it. :)
9 – Ans: B. Terminal velocity is reached when air resistance equals the force of gravity (this is constant since the mass of the body is constant). So, it depends on the mass of the body. Since the mass is related to density and volume (shape), the terminal velocity is affected by all three. Since the question says that the terminal velocity IS reached, the height is not relevant here.

10 – Ans: C. The force on a body is DEFINED as the rate of change of momentum of the body. This does equal to the product of mass and acceleration but for A-Level, this is NOT accepted as a DEFINITION.

30 – Ans: C. Interference pattern is only along XY (although there can be 1 along PQ, but this was not an option). Note that waves are produced at P and Q. Phase difference between waves from P and Q is constant along line RS (since waves are coherent and RS is midway from P and Q), so there can be no interference pattern along RS. From this, ans A, B and D are eliminated.

32 – Ans: C. Force = total EQ = E(+Q) + E(-Q) = 0. Electric field is from +ve to –ve. So, charge +Q will go downwards while charge –Q will go upwards (unlike charges attract) causing a resultant anti-clockwise torque.

33 – Ans: A. R = ρL/A. So, resistivity ρ = RA / L. The electrical resistivity of material is numerically equal to resistance in ohms of a cube of that material, cube being of side length 1 metre (since length is 1m, both A and L in above equation is 1. So, ρ = R) and resistance being measured between opposite faces.

Answer C is true only if the sample is a wire (consider a cuboid for example, it will have different cross-sectional area – it is known that for a material, the electrical resistivity is constant, independent of the shape of the sample)
Click to expand...

Thanks :)
 
janasalem

janasalem

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A cylindrical tube rolling down a slope of inclination θ moves a distance L in time T. The equation
relating these quantities is
L (3+a^2/P = QT^2sinθ
Where a is the internal radius of the tube and P and Q are constants.
Which line gives the correct units for P and Q?
 
Mahnoorfatima

Mahnoorfatima

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Anna Litical drops a ball from rest from the top of 78.4-meter high cliff. How much time will it take for the ball to reach the ground and at what height will the ball be after each second of motion?
I don't get the second part where the question says at what height will the ball be after each second of motion? The solution goes like:
At t = 1 s, y = 4.9 m (down) so height is 73.5 m (78.4 m - 4.9 m )

At t = 2 s, y = 19.6 m (down) so height is 58.8 m (78.4 m - 19.6 m )

At t = 3 s, y = 44.1 m (down) so height is 34.3 m (78.4 m - 45 m)

At t = 4 s, y = 78.4 m (down) so height is 0 m (78.4 m - 78.4 m)
Why are we subtracting 4.9 for the 1st second?
 
Mahnoorfatima

Mahnoorfatima

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