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marin [14]
3 years ago
8

A rock dropped from a 20 meter bridge falls into the river below. How long did it take to reach the water? What velocity did it

hit the water with.
Physics
1 answer:
Brut [27]3 years ago
6 0

Answer:

2 s, -20 m/s

Explanation:

Given:

y₀ = 20 m

y = 0 m

v₀ = 0 m/s

a = -9.8 m/s²

Find: t and v

y = y₀ + v₀ t + ½ at²

0 = 20 + 0 + ½ (-9.8) t²

0 = 20 − 4.9 t²

t ≈ 2 s

v² = v₀² + 2a(y − y₀)

v² = 0 + 2(-9.8)(0 − 20)

v ≈ ±20 m/s

Since the rock is falling, v = -20 m/s.

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Describe the factors that cause static friction between two surfaces to increase.
maw [93]

Answer : The static friction depends on two factors

1. Roughness of the surface

2. Force

Explanation : Friction occur when surface is not smooth.

The formula of friction is

F= \mu mg

Static friction depends on the roughness of the surface and force which is trying to push to object along the surface.

Static friction is caused by the attraction between two surfaces that are in contact.  when the surface will rough and the object will heavier then the force will be larger.

4 0
3 years ago
A coffee filter of mass 1.5 grams dropped from a height of 3 m reaches the ground with a speed of 0.7 m/s. How much kinetic ener
Mademuasel [1]

The kinetic energy gained by the air molecules is 0.0437 J                

<h3 />

Given:

Mass of a coffee filter, m = 1.5 g

Height from which it is dropped, h = 3 m

Speed at ground, v = 0.7 m/s

Initially, the coffee filter has potential energy. It is given by :

P =mgh

P = 1.5 × 10⁻³ kg × 9.8 m/s² × 3m

P = 0.0441 J

Finally, it will have kinetic energy. It is given by :

E= \frac{1}{2} mv^{2}

E= \frac{1}{2}×1.4 × 10⁻³ × (0.7)²

E = 0.000343 J

The  kinetic energy Kair did the air molecules gain from the falling coffee filter is :

E = 0.000343 -  0.0441

  = 0.0437 J

So, the kinetic energy Kair did the air molecules gain from the falling coffee filter is 0.0437 J

Learn more about kinetic energy here:

brainly.com/question/8101588

#SPJ4

8 0
2 years ago
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Lady bird [3.3K]

Answer:

Explanation:

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8 0
3 years ago
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Chinese public buildings erected under a construction code of the Sung dynasty have withstood earthquakes well because the white
luda_lava [24]

Answer:

A: used has four times the tensile strength of steel and the timber frame, incorporating

Explanation:

Option A is correct because it conveys the correct message intended by the statement and has no grammatical errors.

Option B is wrong because to say "has four times the tensile strength of steel has" is just grammatically and idiomatically wrong as has is used twice in the sentence.  

Option C is wrong because the statement that has to do with the flexibility of the timber's frame is more like a separate fact and does not fall under the scope of trying to further explain a fact.

Option D is wrong because it has the same problem in Option C. The comma that is placed after "steel" breaks the sentence and hence does not provide a good understanding of why the building can withstand earthquakes.

Option E is grammatically wrong for using does in the sentence "has four times the tensile strength steel does"

8 0
3 years ago
What are two ways to change the state of a substance?
weeeeeb [17]
Solid to liquid
Liquid to solid

By adding or removing heat energy aka thermal energy 
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