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marin [14]
4 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]4 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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A lightweight string is wrapped several times around the rim of a small hoop. If the free end of the string is held in place and
MariettaO [177]

Answer:

Explanation:

Let T be the tension

For linear motion of hoop downwards

mg -T = ma , m is mass of the hoop . a is linear acceleration of CG of hoop .

For rotational motion of hoop

Torque by tension

T x R ,      R is radius of hoop.

Angular acceleration be α,

Linear acceleration a = α R

So TR = I  α

= I  a / R

a = TR² / I

Putting this value in earlier relation

mg -T = m TR² / I

mg = T ( 1 + m R² / I )

T = mg / ( 1 + m R² / I )

mg / ( 1 + R² / k² )

Tension is less than mg or weight because denominator of the expression is more than 1.

5 0
3 years ago
Air is enclosed in a syringe at room temperature. The end is the pushed so the air only fills a 1/3 of the length of the syringe
borishaifa [10]

Answer:

A) Does not change

B) Decrease

C) Increasing

D) Increasing

Explanation:

When it pushes it's volume is reduced by 1/3 because it's Area is constant there for only volume is decreased. Then the number of molecules don't change

A) don,t change

B) Decreases

C) Density is increased because it mass doesn't change. there for

Mass = Density * Volume

When Volume is decreasing to keep mass constant Density will be increased.

D) Pressure is increased according to the boil's law. it says that for fixed mass and fixed temperature pressure is inversely proportional to the volume. then volume decrease pressure increase  

4 0
3 years ago
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In this graph, calculate the speed of<br> segment A in m/s?
andrew11 [14]

Answer:

The answer is Speed=2m/s

Explanation:

S=D/T

S=10m/5s

S=2m/s

5 0
3 years ago
An object becomes positively charged when it
goldfiish [28.3K]

Answer:

A. loses an electron, it becomes positively charged.

5 0
3 years ago
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An African elephant can heights of 4m and possess a mass of as much as 6000kg. Determine the weight of an African elephant in Ne
Alexandra [31]

The weight of the African elephant is 58,800 Newtons.

Explanation:

Step 1:

Mass of the African Elephant = 6000 Kg

We need to find the weight of  African elephant in Newton.

Step 2 :

Weight in Newtons = Mass of the object ×  acceleration due to gravity (g)

We know that value of  g is 9.8 m/sec²

Hence the required weight = 6000 × 9.8 = 58,800 Newtons

The height of the elephant can reach 4 m. But the weight of any object is nit dependent on the height and hence this information is not required to compute the weight.

Step 3 :

Answer :

The weight of the African elephant is 58,800 Newtons.

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3 years ago
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