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My physics teachers have being boring all my life, but my current teacher is good and what is the point of science when you belive in a religion?

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help please..

 

A narrow pencil enters the top of the water in a rectangular aquarium at and angle of incidence of 40 degrees. The refrcated pencil continues to the bottom of the tank, striking a horizonatally placed plane mirror which refletcs it back again to the surface, and it is again refracted as it emerges into the air

 

1) what is the angle between the incident ray entering the wtaer and the refracted ray emerging from the water?

2) If the water tank is 10 cm deep, what is the distance between the points on the water surface where the ray enters and where it emerges.

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My physics teachers have being boring all my life, but my current teacher is good and what is the point of science when you belive in a religion?

 

Contrary to popular belief, science and religion do not contradict each other. In fact, they co-exist and support each other. Read 'Angels and Demons' by Dan Brown. Or well, more importantly, Quran :P

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Please help with whichever you can, anyone.

 

1) A spring with spring constant k is hung vertically. A mass m is gently attached to it and released in such a way that the spring is unstretched upon release. The mass descends to a maximum spring extension X. Determine the maximum speed of the mass in terms of m, k, and g.

The answer is ((mg^2)/k)^1/2 How do you get that?

 

2) A steel ring has 3 inches inside diameter at 20 degrees Celsius. It is to be heated and slipped over a brass shaft of 3.002 inches diameter at 20 degrees C. I fthe ring and shaft together are cooled by some means such as liquid air, at what temperature will the ring just slip off the shaft?

Answer is -63.2 degrees. I sort of understand this but not thoroughly.

 

3) What must be the initial veocity of a lead bullet at a temp. of 25 Celsius so that the heat developed when it is brought to rest shall be just sufficient to melt it?

Answer is 357 m/s . All my attempts got me completely different answers, so I have no idea on this one.

 

4) A certain house burns 10 tons of coal in a heating season. The heat of combustion of the coal is 11,000 Btu/lb. If stack losses are 15%, how many Btu were actually used to heat the house?

Answer: 1.87E8 Btu

 

5) In some localities large tanks of water are heated by solar radiation during the summer and the stored energy is used for heating during the winter. Find the required dimensions of the storage tank, assuming it to be a cube, to store a quantity of energy equal to that computed in #4. Assume the water is raised to 120 fahrenheit in the summer and cooled to 80 farenheit in the winter.

Answer: 12.8 m

 

I obviously have the answers, but I don't know how to get them. Any help would be greatly appreciated.

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physics is the mother/father/grandfather of all sciences.

There's a reason people with the highest i.q's are often physicists! :D

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Please help with whichever you can, anyone.

 

1) A spring with spring constant k is hung vertically. A mass m is gently attached to it and released in such a way that the spring is unstretched upon release. The mass descends to a maximum spring extension X. Determine the maximum speed of the mass in terms of m, k, and g.

The answer is ((mg^2)/k)^1/2 How do you get that?

 

2) A steel ring has 3 inches inside diameter at 20 degrees Celsius. It is to be heated and slipped over a brass shaft of 3.002 inches diameter at 20 degrees C. I fthe ring and shaft together are cooled by some means such as liquid air, at what temperature will the ring just slip off the shaft?

Answer is -63.2 degrees. I sort of understand this but not thoroughly.

 

3) What must be the initial veocity of a lead bullet at a temp. of 25 Celsius so that the heat developed when it is brought to rest shall be just sufficient to melt it?

Answer is 357 m/s . All my attempts got me completely different answers, so I have no idea on this one.

 

4) A certain house burns 10 tons of coal in a heating season. The heat of combustion of the coal is 11,000 Btu/lb. If stack losses are 15%, how many Btu were actually used to heat the house?

Answer: 1.87E8 Btu

 

5) In some localities large tanks of water are heated by solar radiation during the summer and the stored energy is used for heating during the winter. Find the required dimensions of the storage tank, assuming it to be a cube, to store a quantity of energy equal to that computed in #4. Assume the water is raised to 120 fahrenheit in the summer and cooled to 80 farenheit in the winter.

Answer: 12.8 m

 

I obviously have the answers, but I don't know how to get them. Any help would be greatly appreciated.

 

 

1. at the max spring extention: mgX = 1/2 k X^2 --> X = 2mg/k

omega = sqrt(k/m) amp = X

for oscilations, max speed = amp * omega

 

 

3. find the melting point of lead; T

 

heat to melt lead; Q = m c (T-25)

equivelent KE = 1/2 m V^2

 

equate KE and Q, and solve for V

 

4. find 10 tons is lbs. say m

raw heat produced with it ; H = m * 11000 btu

actual heat = H*85%

 

5. Volume V = x^3 (x=side of cube)

find temp difference in Celcius, say T

c = specific heat capacity

mass of water = V * density

Heat loss H = mass * c * T

 

 

solve for x

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2. find expansitivity of steel and brass

initially both are at same temp; 20 and both have linear lenght 3 inches L

 

new length at temp T

 

L_new_steel = L (1+alpha_steel (T-20))

L_new_brass = L (1+alpha_brass (T-20))

 

at slipping point; L_new_brass = L_new_steel

solve for T

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Thank you. I'm still looking through them, but I keep getting the wrong anser for #3. What am I doing wrong?

 

KE = Qtotal

1/2 m v ^2 = mc(T2-T1) + m Hf

v = [2c (T2-T1) +2 Hf] ^1/2

 

c= .130 j/g Celsius

T2 = 327.3 Celsius

T1 = 25 Celsius

Hf = 24.5 j/g

 

= 11.3 m/s

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Regarding #1, we were doing these kinds of problems without omega and angular motion.

 

Here's the diagram:

uri3s.jpg

 

 

The answer key uses this method:

Vmax is when gravity force (mg) = spring force (kx); when x = mg/k

Eo = Ef

mgx = 1/2 mv ^2 + 1/2 kx^2

Plug in x's and solve for v.

 

But I don't understand how or why gravitational potential is Eo and it equals kinetic plus elastic potential.

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