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MakcuM [25]
4 years ago
13

When determining whether a chemical reaction has taken place, you observe and look for several indicators. Which would be consid

ered an indication that a chemical reaction or chemical change has taken place? A) Solid melts. B) Heat is given off. C) Substance dissolves D) Substance changes shape.
Physics
1 answer:
Inga [223]4 years ago
6 0
The answer is B.

A cannot be the answer is melting is a physical change. No chemical reaction took place.

B is the answer as it is a EXOTHERMIC REACTION so heat will be given off.

C cannot be the answer as dissolving is basically atoms becoming ions, not a chemical reaction whereby a reactant reacts with another reactant to form a product.

D cannot be the answer. Same reason as for why A is not the answer.

Cheers.
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When this circuit is closed, which way do the electrons flow?
gizmo_the_mogwai [7]

Answer:

from the positive end of the battery through the capacitor through the resistors to the negative end...

Current flows from higher potential (+) to lower potential (-)..

3 0
3 years ago
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As demonstrated by the Doppler Effect, why does sound increase in pitch as a sound source approaches you?
scZoUnD [109]
I think so it ans wold be d.because if the source approaches the observer more and more wavefront will pass and it get squeezed.so wavelength decreases and frequency increases.
3 0
3 years ago
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In the Bohr model of hydrogen, the electron moves in a circular orbit around the nucleus. (a) Determine the orbital frequency of
Airida [17]

Answer:

(a) 6.567 * 10^15 rev/s or hertz

(b) 8.21 * 10^14 rev/s or hertz

Explanation:

Fn= 4π^2k^2e^4m * z^2/(h^3*n^3)

Where Fn is frequency at all levels of n.

Z = 1 (nucleus)

e = 1.6 * 10^-19c

m = 9.1 * 10^-31 kg

h = 6.62 * 10-34

K = 9 * 10^9 Nm2/c2

(a) for groundstate n = 1

Fn = 4 * π^2 * (9*10^9)^2*(1.6*10^-19)^4* (9.1 * 10^-31) * 1 / (6.62 * 10^-31)^3 = 6.567 * 10^15 rev/s

(b) first excited state

n = 1

We multiple the groundstate answer by 1/n^3

6.567 * 10^15 rev/s/ 2^3

F2 = 8.2 * 10^ 14 rev/s

3 0
3 years ago
If you have 10.0 g of a substance that decays with a half-life of 14 days, then how much will you have after 42 days?
Nat2105 [25]
The formula for the mass that remains:
m=m_0 \times (\frac{1}{2})^\frac{t}{T}
m₀ - the initial mass, t - time, T - the half-life

m_0=10 \ g \\
T=14 \ d \\
t=42 \ d \\ \\
m=10 \times (\frac{1}{2})^\frac{42}{14}=10 \times (\frac{1}{2})^3=10 \times \frac{1}{8}=10 \times 0.125=1.25

The answer is c. 1.25 g.
6 0
3 years ago
where σ(t) and σ(0) represents the time-dependent and initial (i.e., time =0) stresses, respectively, and t and τ denote elapsed
lesya [120]

Answer:

E_r(6)=4.35614\ MPa

Explanation:

\epsilon = Strain = 0.49

\sigma _0 = 3.1 MPa

At t = Time = 32 s \sigma = 0.41 MPa

\tau = Time-independent constant

Stress relation with time

\sigma=\sigma _0exp\left(-\frac{t}{\tau}\right)

at t = 32 s

0.41=3.1exp\left(-\frac{32}{\tau}\right)\\\Rightarrow exp\left(-\frac{32}{\tau}\right)=\frac{0.41}{3}\\\Rightarrow -\frac{32}{\tau}=ln\frac{0.41}{3}\\\Rightarrow \tau=-\frac{32}{ln\frac{0.41}{3}}\\\Rightarrow \tau=16.0787\ s

The time independent constant is 16.0787 s

E_{r}(t)=\frac{\sigma(t)}{\epsilon_0}

At t = 6

\\\Rightarrow E_{r}(6)=\frac{\sigma(6)}{\epsilon_0}

From the first equation

\sigma(t)=\sigma _0exp\left(-\frac{t}{\tau}\right)\\\Rightarrow \sigma(6)=3.1exp\left(-\frac{6}{16.0787}\right)\\\Rightarrow \sigma(6)=2.13451

E_r(6)=\frac{2.13451}{0.49}\\\Rightarrow E_r(6)=4.35614\ MPa

E_r(6)=4.35614\ MPa

6 0
3 years ago
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