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zhannawk [14.2K]
3 years ago
11

A man can row a boat at 4kmhr in still water. He rows the boat 2km upstream and 2 km back to his starting place in 2 hours. How

fast is the stream flowing
Physics
1 answer:
Softa [21]3 years ago
3 0

Answer:

2.83km/hr

Explanation:

Let stream flowing at the rat x km/hr

In still water

Speed of boat=4km/hr

Upstream speed=4-x

Downstream speed=4+x

Total time=2 hr

Time=Distance/speed

According to question

\frac{2}{4+x}+\frac{2}{4-x}=2

\frac{8-2x+8+2x}{(4+x)(4-x)}=2

\frac{16}{4^2-x^2}=2

Using the formula

(a+b)(a-b)=a^2-b^2

4^2-x^2=\frac{16}{2}

16-x^2=8

16-8=x^2

8=x^2

x=\sqrt{8}=2.83km/hr

Hence, the stream  is flowing at 2.83km/hr

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A spy satellite uses a telescope with a 1.7-m-diameter mirror. It orbits the earth at a height of 180 km.
WINSTONCH [101]

Answer: the minimum spacing that must be there between two objects on the earth's surface if they are to be resolved as distinct objects by this telescope 6.45 cm

Explanation:

Given that;

diameter of the mirror d = 1.7 m

height h = 180 km = 180 × 10³ m

wavelength λ = 500 nm = 5 × 10⁻⁹ m

Now Angular separation from the peak of the central maximum is expressed as;

sin∅= 1.22 λ / d

sin∅ = (1.22 × 5 × 10⁻⁹) / 1.7

 sin∅ = 3.588 × 10⁻⁷

we know that;

 sin∅  = object separation / distance from telescope

object separation =   sin∅ × distance from telescope

object separation = 3.588 × 10⁻⁷  × 180 × 10³

object separation =6.45 × 10⁻² m

then we convert to centimeter

object separation = 6.45 cm

Therefore the minimum spacing that must be there between two objects on the earth's surface if they are to be resolved as distinct objects by this telescope 6.45 cm

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3 years ago
What is NOT a principle of genetics?
timurjin [86]

The recessive trait will always show up

3 0
3 years ago
Read 2 more answers
You should increase the distance between your car and the vehicle ahead when you:
ELEN [110]
<span>You should increase the distance between your car and the vehicle ahead when you are being tailgated by another driver.
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8 0
3 years ago
A satellite is orbiting Earth in an approximately circular path. It completes one revolution each day (86,400 seconds). Its orbi
stira [4]
@AL2006 had answered this before: Well, first of all, wherever you got this question from has done 
a really poor job of question-writing.  There are a few assorted 
blunders in the question, both major and minor ones:

-- 22,500 is the altitude of a geosynchronous orbit in miles, not km.

-- That figure of 22,500 miles is its altitude above the surface, 
   not its radius from the center of the Earth. 

-- The orbital period of a synchronous satellite has to match 
    the period of the Earth's rotation, and that's NOT 24 hours.  
    It's about 3 minutes 56 seconds less ... about 86,164 seconds. 

Here's my solution to the question, using some of the wreckage 
as it's given, and correcting some of it.  If you turn in these answers
as homework, they'll be marked wrong, and you'll need to explain 
where they came from.  If that happens, well, serves ya right for
turning in somebody else's answers for homework.


The satellite is traveling a circle. The circle's radius is 26,200 miles
(not kilometers) from the center of the Earth, so its circumference 
is (2 pi) x (26,200 miles) = about 164,619 miles.

    Average speed = (distance covered) / (time to cover the distance)

                             = (164,619 miles) / day
                                (264,929 km)

                             =      6,859 miles per hour
                                  (11,039 km) 

                           =          1.91 miles per second
                                      (3.07 km)
6 0
3 years ago
Stars are classified mainly according to their distance from Earth.
Zielflug [23.3K]
 The answer is b) false. Stars are mainly classified by their spectra (the elements they absorb) and their temperature.
4 0
3 years ago
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