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3 years ago

Which statement is a characteristic of a concave lens?

Physics

2 answers:

diamong [38]3 years ago

6 0

I think the answer would be D

Trava [24]3 years ago

3 0

D. it is thickest in the middle

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You are trying to overhear a juicy conversation, but from your distance of 20.0 m , it sounds like only an average whisper of 30

12345 [234]

Answer:

r₂ = 0.2 m

Explanation:

given,

distance = 20 m

sound of average whisper = 30 dB

distance moved closer = ?

new frequency = 80 dB

using formula

$\beta = 10 log(\dfrac{I_1}{I_0})$

I₀ = 10⁻¹² W/m²

now,

$30 = 10 log(\dfrac{I_1}{10^{-12}})$

$\dfrac{I_1}{10^{-12}}= 10^3$

$I_1= 10^{-8}\ W/m^2$

to hear the whisper sound = 80 dB

$80 = 10 log(\dfrac{I_2}{10^{-12}})$

$\dfrac{I_2}{10^{-12}}= 10^8$

$I_2= 10^{-4}\ W/m^2$

we know intensity of sound is inversely proportional to square of distances

$\dfrac{I_1}{I_2}=\dfrac{r_2^2}{r_1^2}$

$\dfrac{10^{-8}}{10^{-4}}=\dfrac{r_2^2}{20^2}$

$10^{-4}=\dfrac{r_2^2}{20^2}$

r₂ = 0.2 m

6 0

3 years ago

ohms Long describes the relationship between electronic current voltage and ___

levacccp [35]

Answer:

voltage ,current and resistance

5 0

3 years ago

When you set a heavy bag down on the ground, you are doing _______ work on it.

puteri [66]

When you set a heavy bag down on the ground, you are doing negative work on it.

4 0

2 years ago

You are explaining to friends why astronauts feel weightless orbiting in the space shuttle, and they respond that they thought g

bezimeni [28]

Answer:

It's only 1.11 m/s2 weaker at 400 km above surface of Earth

Explanation:

Let Earth radius be 6371 km, or 6371000 m. At 400km above the Earth surface would be 6371 + 400 = 6771 km, or 6771000 m

We can use Newton's gravitational law to calculate difference in gravitational acceleration between point A (Earth surface) and point B (400km above Earth surface):

$g = G\frac{M}{r^2}$

where G is the gravitational constant, M is the mass of Earth and r is the distance form the center of Earth to the object

$\frac{g_B}{g_A} = \frac{GM/r^2_B}{GM/r^2_A}$

$\frac{g_B}{g_A} = \left(\frac{r_A}{r_B}\right)^2$

$\frac{g_B}{g_A} = \left(\frac{6371000}{6771000}\right)^2$

$\frac{g_B}{g_A} = 0.94^2 = 0.885$

$g_B = 0.885 g_A$

So the gravitational acceleration at 400km above surface is only 0.885 the gravitational energy at the surface, or 0.885*9.81 = 8.7 m/s2, a difference of (9.81 - 8.7) = 1.11 m/s2.

6 0

3 years ago

2 kg steel ball is dropped straight down ont a hard horixontal florr and bounces straight up . the balls speed just before and j

Rainbow [258]

Answer:

$40 \frac{kg*m}{s}$

Explanation:

Impulse-momentum theorem states that impulse is equal to the change of momentum:

$\overrightarrow{J}=\overrightarrow{p}_{f}-\overrightarrow{p}_{i}$ (1)

with pf the final momentum and pi the initial momentum. Knowing that momentum is mass (m) times velocity (1) is:

$\overrightarrow{J}=m \overrightarrow{v}_{f}- m \overrightarrow{v}_{i}$

It's important to note that we're dealing with vector quantities so direction matters. If we choose towards the floor positive direction then the initial velocity is positive and the final velocity is negative, so:

$\overrightarrow{J}=-(2kg)(10\frac{m}{s}) - (2.0kg)(10\frac{m}{s})$

$\overrightarrow{J}=-40 \frac{kg*m}{s}$

So, the impulse delivered to the floor is $40 \frac{kg*m}{s}$

5 0

3 years ago