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3 years ago

We can block light by placing obstacles in its path, but it’s much more difficult to block sound. Why?

2 answers:

8 0

It's harder to block sound because sound waves and transverse waves, causing the sound to bounce off objects. This isn't the same with light. Hope that helps.

rjkz [21]3 years ago

5 0

All we have to do is focus on what you want to hear and you can tell your mind to block everything out and its very easy to block light than noise all you have to do is focus

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A 19.12 g mixture of Ca(NO3)2 and KCl is dissolved in 149 g of water. The freezing point of the solution was measured as −5.77 ∘

hichkok12 [17]

Answer:

The mass percentage of calcium nitrate is 31.23%.

Explanation:

Let the the mass of calcium nitrate be x and mass of potassium chloride be y.

Total mass of mixture = 19.12 g

x + y = 19.12 g..(1)

Mass of solvent = 149 g = 0.149 kg

Freezing point of the solution, $T_f$ = -5.77 °C

Molal freezing constant of water = 1.86 °C/m =1.86 °C/(mol/kg)

The van't Hoff factor contribution by calcium nitrate is 3 and by potassium chloride is 2.So:

i = 3

i' = 2

Freezing point of water = T = 0°C

$\Delta T_f=T-T_f=0^oC-(-5.77^oC)=5.77^oC$

$\Delta T_f=i\times K_f\times m$

$Molality=m(mol/kg)=\frac{\text{Moles of solute}}{\text{mass of solvent in kg}}$

$5.77^oC=1.86 ^oC/(mol/kg)\times (\frac{ i\times x}{164 g/mol\times 0.149 kg}+\frac{i'\times y}{74.5 g/mol0.149 kg})$

On solving we get:

$\frac{3x}{164 g/mol}+\frac{2x}{74.5 g/mol}=0.4622 mol$ ....(2)

Solving equation (1)(2) for x and y:

x =5.973 g

y = 13.147 g

Mass percent of $Ca(NO_3)_2$ in the mixture:

$\frac{x}{19.21 g}\times 100=\frac{5.973 g}{19.12 g}=31.23\%$

The mass percentage of calcium nitrate is 31.23%.

5 0

3 years ago

Waves disturb ____, but do not transmit it

Agata [3.3K]

Answer:

energy

Explanation:

im sure

5 0

3 years ago

A lady holds a large concave mirror of focal length 1.8m from her face.State two characteristics of her image in the mirror.

Vlada [557]

Answer:

reflection and refraction?

Explanation:

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Kit

6 0

3 years ago

A 50-cm3 block of wood is floating on water, and a 50-cm3 chunk of iron is totally submerged in the water. Which one has the gre

ludmilkaskok [199]

Answer:

Iron

Explanation:

The buoyant force equals to the weight of water being displaced by the object.

Since, the volume of both iron and wood is equal and the wood is not completely submerged, but the iron block is completely submerged i.e more volume of the water is being displaced by the iron block.

Hence, the buoyant force is more on the iron.

4 0

3 years ago

If an object is dropped from a height of meters, the velocity (in ) at impact is given by v= √2gh , where g=9.8m/sec^2 is the ac

Neporo4naja [7]

Answer:

A.) V = 14 m/s

B.) h = 36.6 m

Explanation:

Given the formula v = √2gh

where g = 9.8m/sec^2 is the acceleration due to gravity.

A.) Determine the impact velocity for an object dropped from a height of 10 m.

Substitute height h in the given formula

V = √2gh

V = √2 × 9.8 × 10

V = √196

V = 14 m/s

b. Determine the height required for an object to have an impact velocity of 26.8 m/sec (~ 60 mph). Round to the nearest tenth of a meter.

Substitute the velocity in the given formula and make height h the subject of formula.

26.8 = √2 × 9.8 × h

Square both sides

718.24 = 19.6h

h = 718.24 / 19.6

h = 36.64 m

h = 36.6 m

5 0

3 years ago