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Sophie [7]
3 years ago
6

A boy standing on a bridge above a river throws stone A vertically upward with an initial velocity =15m/s.2 seconds later he dro

ps stone B with initial velocity=0.Both stones reach the river at the same time.
1-how many seconds does it take stone A to reach the river?
2-how high is the bridge?
3-what is the speed of stone A just before it strikes the river
Physics
1 answer:
Anastaziya [24]3 years ago
7 0

I'm not sure if this is correct but it's what I'll do

This is free-fall problem.
Stone A is thrown upward, at the point it falls down to the place where it was thrown, the velocity is -15m/s.

Now I choose the bridge is the origin. From the bridge, stone A and B fall the same distance which means Ya = Yb ( vertical distance )

Ya = Vo(t + 2) + 1/2a(t+2)^2
= -15(t + 2) + 1/2(9.8)(t^2 + 4t + 4)
= -15t - 30 + 4.5(t^2 + 4t + 4)
= -15t - 30 + 4.5t^2 + 18t + 18
= 4.5t^2 +3t - 12

Yb = Vo(t) + 1/2a(t)^2
= 0 + 4.5t^2

4.5t^2 = 4.5t^2 +3t - 12
0 = 3t - 12
4 = t

Time for Stone B is 4s
Time for Stone A is 6s

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Hatshy [7]

An Excerpt from “Optimism”

by Helen Keller

1 Could we choose our environment, and were desire in human undertakings synonymous with

endowment, all men would, I suppose, be optimists. Certainly most of us regard happiness as

the proper end of all earthly enterprise. The will to be happy animates alike the philosopher, the

prince and the chimney-sweep. No matter how dull, or how mean, or how wise a man is, he feels

that happiness is his indisputable right.

2 It is curious to observe what different ideals of happiness people cherish, and in what singular

places they look for this well-spring of their life. Many look for it in the hoarding of riches, some

in the pride of power, and others in the achievements of art and literature; a few seek it in the

exploration of their own minds, or in the search for knowledge.

3 Most people measure their happiness in terms of physical pleasure and material possession.

Could they win some visible goal which they have set on the horizon, how happy they would be!

Lacking this gift or that circumstance, they would be miserable. If happiness is to be so

measured, I who cannot hear or see have every reason to sit in a corner with folded hands and

weep. If I am happy in spite of my deprivations, if my happiness is so deep that it is a faith, so

thoughtful that it becomes a philosophy of life,—if, in short, I am an optimist, my testimony to

the creed of optimism is worth hearing....

4 Once I knew the depth where no hope was, and darkness lay on the face of all things. Then

love came and set my soul free. Once I knew only darkness and stillness. Now I know hope and

joy. Once I fretted and beat myself against the wall that shut me in. Now I rejoice in the

consciousness that I can think, act and attain heaven. My life was without past or future; death,

the pessimist would say, “a consummation devoutly to be wished.” But a little word from the

fingers of another fell into my hand that clutched at emptiness, and my heart leaped to the

rapture of living. Night fled before the day of thought, and love and joy and hope came up in a

passion of obedience to knowledge. Can anyone who has escaped such captivity, who has felt

the thrill and glory of freedom, be a pessimist?

5 My early experience was thus a leap from bad to good. If I tried, I could not check the

momentum of my first leap out of the dark; to move breast forward is a habit learned suddenly

at that first moment of release and rush into the light. With the first word I used intelligently, I

learned to live, to think, to hope. Darkness cannot shut me in again. I have had a glimpse of the

shore, and can now live by the hope of reaching it.

6 So my optimism is no mild and unreasoning satisfaction. A poet once said I must be happy

because I did not see the bare, cold present, but lived in a beautiful dream. I do live in a

beautiful dream; but that dream is the actual, the present,—not cold, but warm; not bare, but

furnished with a thousand blessings. The very evil which the poet supposed would be a cruel

6) Read the last sentence from the text.

Only by contact with evil could I have learned to feel by contrast the beauty of truth and love and goodness.

Explain how Helen Keller develops this idea in the text. Use specific details to

support your answer.

8 0
3 years ago
What is the easiest way to add energy to matter.
zubka84 [21]

Answer:

Explanation:

Heat is probably the easiest energy you can use to change your physical state. The atoms in a liquid have more energy than the atoms in a solid.

4 0
3 years ago
Read 2 more answers
Five identical cylinders are each acted on by forces of equal magnitude. Which force exerts the biggest torque about the central
elena-s [515]

Answer:

<em>From the image, the force as shown in option A will exert the biggest torque on the cylinder about its central axes.</em>

Explanation:

The image is shown below.

Torque is the product of a force about the center of rotation of a body, and the radius through which the force acts. For a given case such as this, in which the cylinders are identical, and the forces are of equal magnitude, the torque at the maximum radius away from the center will exert the maximum torque. Also, the direction of the force also matters. To generate the maximum torque, the force must be directed tangentially away from the circle formed by the radius through which the force acts away from the center. Option A satisfies both condition and hence will exert the most torque on the cylinder.

6 0
4 years ago
A large, metallic, spherical shell has no net charge. It is supported on an insulating stand and has a small hole at the top. A
tino4ka555 [31]

Answer:

(a) Negative Q

(b) Positive Q

Explanation:

Charge is the inherent property of matter due to the transference of electrons.

There are three methods of charging a body.

(i) Charging by friction: When two uncharged bodies rubbed together, then one body gets positive charged and the other is negatively charges it is due to the transference of electrons form one body to another.  

(ii) Conduction: when a charged body comes in contact with the another uncharged body, the uncharged body gets the same charge and the charge is distributed equally.

(iii) Induction: When a uncharged body keep near the charged body, the uncharged body gets the same amount of charge but opposite in sign.  

(a) When a small tack of charge Q is lowered into the hole, then due to the process of induction, the charge on the inner surface of the shell is - Q.

(b) Due to the process of conduction, the charge on the outer surface of the shell is Q.

7 0
3 years ago
A point charge +6q is located at the origin, and a point charge -4q is located on the x-axis at D = 0.530 m. At what location on
belka [17]

Answer:

Explanation:

A point charge (+6q) at the origin I.e at (0,0)

Another point(-4q) charge is located at (0.53m, 0)

Both charges are on the x axis

Where will a third charge be place and it will experience no net force?

Fnet=0 due to charge 3

The location of qo should be at positive x axis, beyond q2(-4q), so has to have a stable charges.

Let the distance of -4q from qo be x

Then from +6q to qo is 0.56+x

The third charge has a charge of q.

Now we need to find Fnet due to charge 3.

Fnet= F13+F23

Let find F13

Let the distance of q1 from charge qo is 0.56+x

Both q1 and q3 are positive, there will be a force of repulsion between them, the F13 will be in the direction of positive x axis

F13=kq1q3/r²

q1= +6q and q3=q

F13=k6qq/(0.56+x)²

F13=k6q²/(0.56+x)²

In vector form

F13=k6q²/(0.56+x)² i

Now let find F23

q2 is negative and q3 is positive, a force or attraction will occur between the two bodies, then the F23 will move in the negative direction of x-axis

Given that, q2=(-4q) and q3=q, r=x

F23=kq1q3/r²

q1= +6q and q3=q

F23=k4qq/x²

F23=k4q²/x²

In vector form

F23=—k4q²/x² i

So, Fnet=F23+F13

Fnet= —k4q²/x²i + k6q²/(0.56+x)² i

Since Fnet=0

Then,

O=—k4q²/x² + k6q²/(0.56+x)²

k4q²/x² = k6q²/(0.56+x)²

Divide through by k2q², then we have

2/x²=3/(0.56+x)²

2(0.56+x)²=3x²

2(0.3136+1.12x+x²)=3x²

0.6272+2.24x+2x²=3x²

3x²-2x²-0.6272-2.24x=0

x²—2.24x—0.6272=0

Using formula method

a =1 b=-2.24 and x=-0.6272

x=-b±sqrt(b²-4ac)/2a

x=2.24±sqrt(-2.24²-4×1×-0.6272)/2×1

x=2.24±sqrt(5.0176+2.5088)/2

x=2.24±sqrt(7.5264)/2

x=(2.24±2.74)/2

Then x=(2.24+2.74)/2

x=2.49

or x=(2.24-2.74)/2

x=-0.25

So, x will be at (0.53+x) from the origin

1. When x =2.49

(0.53+2.49)=3.02m

2. When x =-0.25

This will not be possible because it will be attracted by the charges.

x=-0.25+0.53

x=0.28m

7 0
4 years ago
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