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Darina [25.2K]
2 years ago
11

The apparent brightness of stars in general tells us nothing about their distances; we cannot assume that the dimmer stars are f

arther away. In order for the apparent brightness of a star to be a good indicator of its distance, all the stars would have to be:__________.
a. at the same distance
b. the same composition
c. the same luminosity
d. by themselves instead of in binary or double-star systems
e. a lot farther away than they presently are
Physics
1 answer:
antoniya [11.8K]2 years ago
3 0
The answer is have the same luminosity
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Assume you need to design a hydronic system that can deliver 80,000 Btu/hr. What flow rate of water is required if the temperatu
PolarNik [594]

Answer:

At 10°F change in temperature

Mass flowrate = 1.01 kg/s = 2.227 lbm/s

Volumetric flowrate = 1010 m³/s = 35667.8 ft³/s

At 20°F change in temperature

Mass flowrate = 0.505 kg/s = 1.113 lbm/s

Volumetric flowrate = 505 m³/s = 17833.9 ft³/s

Explanation:

80000 btu/hr = 23445.7 W

P = ṁc(ΔT)

ṁ = MASS flowrate

c = specific heat capacity of water = 4182 J/kg.K,

ΔT = change in temperature = 10°F

To convert, a change of 18°F is equal to a change of 10°C

A change of 10°F = 10×10/18 = 5.556°C = 5.556K

P = ṁc(ΔT)

23445.7 = ṁ(4182 × 5.556)

ṁ = 23445.7/(4182 × 5.556)

ṁ = 1.01 kg/s = 2.227 lbm/s

In volumetric flow rate, Q = density × mass flowrate = 1000 × 1.01 = 1010 m³/s = 35667.8 ft³/s

For a change of 20°F,

ΔT = change in temperature = 20°F

To convert, a change of 18°F is equal to a change of 10°C

A change of 20°F = 20×10/18 = 11.1111°C = 11.111K

P = ṁc(ΔT)

23445.7 = ṁ(4182 × 11.111)

ṁ = 23445.7/(4182 × 11.111)

ṁ = 0.505 kg/s = 1.113 lbm/s

In volumetric flow rate, Q = density × mass flowrate = 1000 × 0.505 = 505 m³/s = 17833.9 ft³/s

Hope this Helps!!!

4 0
3 years ago
A freight train has a mass of 1.5 X 10^7 kg. If the
Elena L [17]

Answer:

t=444.4s

Explanation:

m=1.5*10^7 kg

F=7.5*10^5 N

v=80km/h*(1h/3600s)*(1000m/1km)=22.22m/s

<u>Second Newton's Law:</u>

F=ma

a=F/m=7.5*10^5/(1.5*10^7)=0.05m/s^2

<u>Kinematics equation:</u>

vf=vo+at=at      

vo: initial velocity equal zero

t=vf/a=22.22/0.05=444.4s

4 0
3 years ago
1. A ball is thrown vertically upward.
Ghella [55]

Answer:

The acceleration increases.

Explanation:

hope this helps

4 0
3 years ago
A rock is dropped from a 110-m-high cliff. How long does it take to fall (a) the first 55.0 m and (b) the second 55.0 m?
Genrish500 [490]

Answer:

a) t = 3.35[s]; b) t = 1.386[s]

Explanation:

We can solve this problem by dividing it into two parts, for the first 55 [m] and then the second part with the remaining 55 [m].

We will take the initial velocity as zero, as the problem does not mention that the Rock was thrown at initial velocity.

And using kinematics equations:

v_{f}^{2}= v_{o}^{2}+2*g*y\\where:\\v_{o}=0\\g=gravity = 9.81[m/s^2]\\y=55 [m]\\v_{f}^{2}=0+2*9.81*55\\v_{f}=\sqrt{2*9.81*55} \\v_{f}=32.85[m/s]

Now we can calculate the time:

v_{f}=v_{o}+g*t\\t=\frac{v_{f}-v_{o}}{g}\\ t=\frac{32.85-0}{9.81}\\ t=3.35[s]

Now we can calculate the second time, but using as a initial velocity 32.85[m/s].

The final velocity will be:

v_{f}^{2}= v_{o}^{2}+2*g*y\\v_{f}=\sqrt{v_{o}^{2}+2*g*y} \\v_{f}=\sqrt{32.85^{2}+2*9.81*55 } \\v_{f}=46.45[m/s]

Now we can calculate the second time:

t=\frac{46.45-32.85}{9.81} \\t= 1.386[s]

Note: The reason the second time is shorter even though it is the same distance is that the acceleration of gravity increases the speed of the rock more and more as it falls.

7 0
3 years ago
A water slide is constructed so that swimmers, starting from rest at the top of the slide, leave the end of the slide traveling
solniwko [45]

Answer:

17.86 m

Explanation:

The first step is to find the velocity of the swimmer.

Velocity, v = s/t

Velocity, v = 5 / 0.27

Velocity, v = 18.52 m/s

Then, we find the height

h = ½gt²

h = ½ * 9.8 * 0.27²

h = 4.9 * 0.0729

h = 0.36 m

Next, we apply the law of conservation of energy

mgH = mgh + ½ mv²

9.8Hm = m(9.8 * 0.36 + 0.5 * 18.52²)

9.8H = 3.528 + 171.4952

9.8H = 175.02

H = 175.02 / 9.8

H = 17.86 m

Therefore, the needed height is 17.86 m

8 0
4 years ago
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