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Phantasy [73]
3 years ago
11

A thermally isolated system consists of a hot piece of aluminum and a cold piece of copper. The aluminum and the copper are in t

hermal contact. The specific heat of aluminum is more than double that of copper. Which object experiences the greater amount of heat transfer during the time it takes the system to reach thermal equilibrium?
a) The aluminum experiences the greater magnitude of heat transfer.
b) The copper experiences the greater magnitude of heat transfer.
c) Both experience the same magnitude of heat transfer.
Physics
1 answer:
RoseWind [281]3 years ago
5 0

Answer:

Explanation:

Make up a question.

The only change is going to be c.

Suppose they aluminum starts our higher at 50oC

Suppose the copper starts out at 20oC

Suppose the mass of both are 25 grams.

Aluminum

m*2c * deltat

  • deltat = 50 - x
  • c = 2*c
  • m = 25

Copper

m*c*deltat

deltat = x - 20

m = 25

c = c

Now since the amount of heat is the same (this starts out on a heated slab of something).

m*2c * (50 - x) = m * c * x - 20  The m and the c are the same. Cancel them out.

2 * (50 - x) = (x - 20)    Remove the brackets.

100 - 2x = x - 20          Add 20 to both sides.

120 - 2x = x                  Add 2x to both sides.

120 = 3x                       Divide by 3

x = 40

What does this tell you?

It tells you that the temperature of the aluminum is only going to drop 10 degrees

The copper is going to gain 40 - 20 = 20  degrees.

The heat transfer is actually the same. It doesn't take as much heat to heat copper as it does aluminum. That's shown by the difference in how the temperature changes. One looses 10 degrees. The other gains 20. The transfer is the same because of the way the "c" operates.        

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Dmitry_Shevchenko [17]
Using the law of conservation of momentum
m1u1+m2u2=m1v1+m2v2
Where m1 is mass of first object
m2 is mass of second object
u1 and u2 are initial velocities of object 1 and 2 respectively
v1 and v2 are final velocities of object 1 and 2 respectively
Here, they are moving as a system after collision. Thus they will posses same final velocity
m1u1 +m2u2=v(m1+m2)
Substituting values
600*4+0=v(600+400)
2400=v*1000
v=2.4 m/s

Now momentum of system
p=Mv
p=(600+400)*2.4
p=1000*2.4
Therefore p=2400 kg m/s
Hope this helps :)
6 0
3 years ago
A 0.5 m diameter wagon wheel consists of a thin rim having a mass of 7 kg and six spokes, each with a mass of 1.2 kg. 1.2 kg 7 k
Arte-miy333 [17]

Explanation:

It is given that,

Mass of the rim of wheel, m₁ = 7 kg

Mass of one spoke, m₂ = 1.2 kg

Diameter of the wagon, d = 0.5 m

Radius of the wagon, r = 0.25 m

Let I is the the moment of inertia of the wagon wheel for rotation about its axis.

We know that the moment of inertia of the ring is given by :

I_1=m_1r^2

I_1=7\times (0.25)^2=0.437\ kgm^2

The moment of inertia of the rod about one end is given by :

I_2=\dfrac{m_2l^2}{3}

l = r

I_2=\dfrac{m_2r^2}{3}

I_2=\dfrac{1.2\times (0.25)^2}{3}=0.025\ kgm^2

For 6 spokes, I_2=0.025\times 6=0.15\ kgm^2

So, the net moment of inertia of the wagon is :

I=I_1+I_2

I=0.437+0.15=0.587\ kgm^2

So, the moment of inertia of the wagon wheel for rotation about its axis is 0.587\ kgm^2. Hence, this is the required solution.

4 0
3 years ago
A gang of robbers is escaping across city roofs at night. They come to the edge of one building and need to drop down to their g
REY [17]

Answer:

a) They will hit the ground with a speed of 19.6 m/s.

b) They are at a height of 20 m.

c) It is not a safe jump.

Explanation:

Hi there!

a) The equations of height and velocity in function of time of a free falling body are the following:

h = h0 + v0 · t + 1/2 · g · t²

v = v0 + g · t

Where:

h = height of the object at time t.

h0 = initial height.

v0 = initial velocity.

t = time.

g = acceleration due to gravity (-9.8 m/s² considering downward as negative direction).

v = velocity of the object at time t.

Using the equation of velocity, let's find the velocity at which they will hit the ground. The pebble is dropped (initial velocity = 0) and it takes 2 s to reach the ground:

v = v0 + g · t     (v0 = 0)

v = g · t

v = -9.8 m/s² · 2.0 s

v = -19.6 m/s

They will hit the ground with a speed of 19.6 m/s.

b)Now, we have to use the equation of height:

h = h0 + v0 · t + 1/2 · g · t²

If we place the origin of the frame of reference on the ground, we have to find the initial height (h0) knowing that at t = 2.0 s, h = 0 m

0 m = h0 - 1/2 · 9.8 m/s² · (2.0 s)²

h0 = 1/2 · 9.8 m/s² · (2.0 s)²

h0 = 20 m

They are at a height of 20 m.

c)According to a NASA paper (Issues on Human Acceleration Tolerance After Long-Duration Space Flights, figure 10), if you fall with a vertical velocity greater than 17 m/s it is unlikely that you will survive. So, it is not a safe jump.  

3 0
3 years ago
Until a train is a safe distance from the station it must travel at 5 m/s. Once the train is on open track it can speed up
kirza4 [7]

Answer:

I believe the answer is b

Explanation:

5 0
3 years ago
Violet light of wavelength 405 nm ejects electrons with a maximum kinetic energy of 0.890 eV from a certain metal. What is the b
AleksandrR [38]

Answer:

  Ф = 2.179 eV

Explanation:

This exercise has electrons ejected from a metal, which is why it is an exercise on the photoelectric effect, which is explained assuming the existence of energy quanta called photons that behave like particles.

            E = K + Ф

the energy of the photons is given by the Planck relation

            E = h f

we substitute

           h f = K + Ф

           Ф= hf - K

the speed of light is related to wavelength and frequency

            c = λ f

            f = c /λ

            Φ = \frac{hc}{\lambda } - K

let's reduce the energy to the SI system

            K = 0.890 eV (1.6 10⁻¹⁹ J / 1eV) = 1.424 10⁻¹⁹ J

calculate

           Ф = 6.63 10⁻³⁴ 3 10⁸/405 10⁻⁹  -1.424 10⁻¹⁹

           Ф = 4.911 10⁻¹⁹ - 1.424 10⁻¹⁹

           Ф = 3.4571 10⁻¹⁹ J

         

we reduce to eV

           Ф = 3.4871 10⁻¹⁹ J (1 eV / 1.6 10⁻¹⁹ J)

           Ф = 2.179 eV

4 0
2 years ago
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