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Physics MCQs thread.

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nerd007

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cocospaniel said:
nerd007 said:
Does anyone know how to solve questions like these? I always get them wrong.

Two wires P and Q are made from the same material.
Wire P is initially twice the diameter and twice the length of wire Q. The same force, applied to
each wire, causes the wires to extend elastically.
What is the ratio of the extension in P to that in Q?
A.1/2 B.1 C.2 D.4

Thanks a lot. You guys have been great =D
Click to expand...

I have wrote this many times
Use the young Modulus formula. E= Fl/Ae
Equation 1 - Ee= F(tension)*l/A
Equation 2 - Ee= F(tension)*2l/0.5A = 4Fl/A

Since it's the same wires, young modulus is the same, (e) is the same. So equate both equations.
Fl/A=4Fl/A Do some algebraic manipulation and you'll get 4/1 :)
Click to expand...


Oops.. sorry. Thanks =D
 
A

aleem420

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27 The interference patterns from a diffraction grating and a double slit are compared.
Using the diffraction grating, yellow light of the first order is seen at 30° to the normal to the
grating.
The same light produces interference fringes on a screen 1.0 m from the double slit. The slit
separation is 500 times greater than the line spacing of the grating.
What is the fringe separation on the screen?
A 2.5 × 10–7m
B 1.0 × 10–5m
C 1.0 × 10–3m
D 1.0 × 10–1m


Plz help................
 
C

cocospaniel

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wonderland said:
URGENT HOW TO DO QUESTION 3 MAY JUNE 2005 AND THE ANSWER IS B
Click to expand...

a 100 m race in the Olympics takes about 10 s
so
v = 10 m/s (avg speed over whole race)
then
KE = 1/2 m v ^2 = 1/2(80)(10)^2 = 4000 J
 
C

cocospaniel

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Zizu1992 said:
Please help me with my problem too :(
Click to expand...

we know d sin(A)=n*lambda
A=30 deg....so sinA=0.5.....we get 0.5d=lambda

X=(Lambda*D)/a
substitute 0.5d for lambda and a ll be 500d
u get fringe separation of 10^-3 m.....i.e option C :)
 
M

mrpaudel

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nerd007 said:
Does anyone know how to solve questions like these? I always get them wrong.

Two wires P and Q are made from the same material.
Wire P is initially twice the diameter and twice the length of wire Q. The same force, applied to
each wire, causes the wires to extend elastically.
What is the ratio of the extension in P to that in Q?
A.1/2 B.1 C.2 D.4

Thanks a lot. You guys have been great =D
Click to expand...

For these type of questions...i strongly suggest u to assume numerical values urself..acc to question..like if it says P has diamater twice than that of Q..than assume diamter of q=2cm...and therefore P=4cm..these assumptions make u easy..!!
 
C

cocospaniel

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aleem420 said:
27 The interference patterns from a diffraction grating and a double slit are compared.
Using the diffraction grating, yellow light of the first order is seen at 30° to the normal to the
grating.
The same light produces interference fringes on a screen 1.0 m from the double slit. The slit
separation is 500 times greater than the line spacing of the grating.
What is the fringe separation on the screen?
A 2.5 × 10–7m
B 1.0 × 10–5m
C 1.0 × 10–3m
D 1.0 × 10–1m


Plz help................
Click to expand...

we know d sin(A)=n*lambda
A=30 deg....so sinA=0.5.....we get 0.5d=lambda

X=(Lambda*D)/a
substitute 0.5d for lambda and a ll be 500d
u get fringe separation of 10^-3 m.....i.e option C :)
 
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