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-InnocentSoul- thumbnail
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Posted: 13 years ago
help in math:l
1). If y varies directly as n ^n with a constant of variation k, and z varies directly as y^m with constant of variation c, then z varies directly as some power of x. what power is it, and what is the constant of variation?

2). The moment of inertia of a solid sphere about a diameter varies jointly with the mass of the sphere and the square of its radius. If a sphere of a mass 10 g and a radius of 3 cm has a moment of inertia of 36g-cm^2, what is the moment of inertia of a 6 g sphere of radius 5cm?

3). If x is jointly proportional to v and w, and x=24 when v=15 and w=8 find x when v=10 and w=6.

4).If v varies directly as the square root of x and inversely as y, and v=18 when x=9 and y=45, find v when x=25 and y=3.

5). if the temperature is kept constant, the volume of an ideal gas is inversely proportional to the pressure on it. At 1.8 atmospheres , a given mass of hydrogen occupies 48m^3. what pressure would be necessary to change this volume to be 30m^3.

6). The Kinetic energy of an object varies jointly as its mass and the square of its velocity. If it takes 50 joules of energy to move a 4kg object at 5m/s, how much energy would be required to move an 8kg object at 10m/s?

7).Suppose z varies jointly as x and y and inversely as w, and z=8 when x=6, y=5, and w=10. find z when x=3, y=4 and w=5.

8). Suppose z varies directly as w and inversely as uv, and z=5 when u=9, v=4 and w=13. find w when z=10, u=6, and v=151.

9). The Gravitational force that the earth exerts on an object varies inversely as the square of its distance frm the center of the earth. If the earth exerts a force of 19,000 N on an orbiter module on the earth's surface, 64,00 km frm the center of the earth, what force would it exert on the module when it is 8000 km frm the earth's center.

10). The attractive force between two oppositely charged particles varies jointly with the magnitude of their charges and inversely as the square of the distance between them. the force between two particles with charge of 5 Micro coulombs and 1 micro coulombs, which are 0.3 m apart, is 0.5 N. what is the force between charges of 2 micro coulombs and 6 micro coulombs that are 0.4 m apart.

11). Suppose z varies jointly as x and y and inversely as w, and z=6 when x =4, y= 5 and w= 8. find z when x=2, y=6 and w=4.

12). Suppose z varies directly as w and inversely as uv, and z=10 when u=8, v=6 and w=4. find w when z=16, u=15 and v=3.

13). The electrostatic force of repulsion between two apha particles varies inversely as the square of the distance between them. If this force is 0.384 newtons when the particles are 0.05 picometers apart, what is the force when the particles are 0.2 picometers apart.

need it by Sunday :D
Edited by priya_94 - 13 years ago
akhl thumbnail
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Posted: 13 years ago
@priya_94
1). If y varies directly as n ^n with a constant of variation k, and z varies directly as y^m with constant of variation c, then z varies directly as some power of x. what power is it, and what is the constant of variation?
y = k x^n
z = c y^m

Therefore,
z = c (k x^n)^m
z = c k^m x^(mn)
Ans: the power is x^(mn) and the constant of variation is c k^m


2). The moment of inertia of a solid sphere about a diameter varies jointly with the mass of the sphere and the square of its radius. If a sphere of a mass 10 g and a radius of 3 cm has a moment of inertia of 36g-cm^2, what is the moment of inertia of a 6 g sphere of radius 5cm?
I/(m*r^2) = constant
36/(10 * 3^2) = I/(6 * 5^2)
36/(10 * 9) = I/(6 * 25)
I = 6 * 25 * 36/(10 * 9)
I = 60 g-cm^2 (Answer)


3). If x is jointly proportional to v and w, and x=24 when v=15 and w=8 find x when v=10 and w=6.
x/(vw) = constant
24/(15*8) = x/(10*6)
1/5 = x/60
x = 60/5
x = 12 (Answer)


4).If v varies directly as the square root of x and inversely as y, and v=18 when x=9 and y=45, find v when x=25 and y=3.
v/sqrt(x) * y = constant
18/sqrt(9) * 45 = v/sqrt(25) * 3
18/3 * 45 = v/5 * 3
18 * 15 = v/5 * 3
v = 18 * 15 * 5/3
v = 450 (Answer)


5). if the temperature is kept constant, the volume of an ideal gas is inversely proportional to the pressure on it. At 1.8 atmospheres , a given mass of hydrogen occupies 48m^3. what pressure would be necessary to change this volume to be 30m^3.
P*V = constant
1.8 * 48 = P*30
P = 1.8 * 48/30
P =
atmospheres (Answer)

Will answer others later, but can you answer yourself too?


Edited by akhl - 13 years ago
-InnocentSoul- thumbnail
14th Anniversary Thumbnail Sparkler Thumbnail
Posted: 13 years ago

Originally posted by: akhl

@priya_94

1). If y varies directly as n ^n with a constant of variation k, and z varies directly as y^m with constant of variation c, then z varies directly as some power of x. what power is it, and what is the constant of variation?
y = k x^n
z = c y^m

Therefore,
z = c (k x^n)^m
z = c k^m x^(mn)
Ans: the power is x^(mn) and the constant of variation is c k^m


2). The moment of inertia of a solid sphere about a diameter varies jointly with the mass of the sphere and the square of its radius. If a sphere of a mass 10 g and a radius of 3 cm has a moment of inertia of 36g-cm^2, what is the moment of inertia of a 6 g sphere of radius 5cm?
I = k m r^2
Putting m = 10, r = 3, I = 36,
36 = k * 10 * 3^2
36 = k * 90
k = 36/90
k = 2/5
Therefore, I = (2/5) * m r^2
Putting m = 6, r = 5,
I = (2/5) * 6 * 5^2
I = 60 g-cm^2 (Answer)


3). If x is jointly proportional to v and w, and x=24 when v=15 and w=8 find x when v=10 and w=6.
x = k v w
Putting x = 24, v = 15, w = 8,
24 = k * 15 * 8
k = 0.2
Therefore, x = 0.2 v w
Puttin v = 10, w = 6,
x = 0.2 * 10 * 6
x = 12 (Answer)


4).If v varies directly as the square root of x and inversely as y, and v=18 when x=9 and y=45, find v when x=25 and y=3.
v = k sqrt(x) /y
Putting v = 18, x = 9, y = 45,
18 = k * sqrt(9) /45
18 = k * 3/45
18 = k * 1/15
k = 18 * 15 = 270

Therefore, v = 270 * sqrt(x) /y
Puttig x = 25, y = 3,
v = 270 * sqrt(25) /3
v = 270 * 5/3
v = 450 (Answer)


5). if the temperature is kept constant, the volume of an ideal gas is inversely proportional to the pressure on it. At 1.8 atmospheres , a given mass of hydrogen occupies 48m^3. what pressure would be necessary to change this volume to be 30m^3.
V = k/P
Puttin V = 48, P = 1.8,
48 = k/1.8
k = 48 * 1.8
V = 48 * 1.8/P
Putting V = 30,
30 = 48 * 1.8/P
P = 48 * 1.8/30
P = 2.88 atmospheres (Answer)

Will answer others later, but can you answer yourself too?



thnks sooo much :D...
yes i tried
akhl thumbnail
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Posted: 13 years ago
@priya_94
6). The Kinetic energy of an object varies jointly as its mass and the square of its velocity. If it takes 50 joules of energy to move a 4kg object at 5m/s, how much energy would be required to move an 8kg object at 10m/s?
K/(m v^2) = constant
50/(4 * 5^2) = K/(8 * 10^2)
50/100 = K/800
1/2 = K/800
K = 800 * 1/2
K = 400 joules (Answer)


7).Suppose z varies jointly as x and y and inversely as w, and z=8 when x=6, y=5, and w=10. find z when x=3, y=4 and w=5.
z/(xy) * w = constant
8/(6*5) * 10 = z/(3*4) * 5
8/3 = z/12 * 5
z = 8/3 * 12/5
z = 6.4 (Answer)


Edited by akhl - 13 years ago
-InnocentSoul- thumbnail
14th Anniversary Thumbnail Sparkler Thumbnail
Posted: 13 years ago

Originally posted by: akhl

@priya_94
6). The Kinetic energy of an object varies jointly as its mass and the square of its velocity. If it takes 50 joules of energy to move a 4kg object at 5m/s, how much energy would be required to move an 8kg object at 10m/s?

K = c * m * v^2
Put K = 50, m = 4, v = 5
50 = c * 4 * 5^2
50 = c * 100
c = 50/100
c = 0.5

K = 0.5 * m * v^2
Put m = 8, v = 10,
K = 0.5 * 8 * 10^2
K = 0.5 * 8 * 100
K = 400 joules (Answer)

7).Suppose z varies jointly as x and y and inversely as w, and z=8 when x=6, y=5, and w=10. find z when x=3, y=4 and w=5.
z = c x y/w
Put z = 8, x = 6, y = 5, w = 10
8 = c * 6 * 5/10
8 = c * 3
c = 8/3
z = (8/3) x y/w
Put x = 3, y = 4, w = 5,
z = (8/3) * 3 * 4/5
z = 6.4 (Answer)


There are two ways to solve such problems. Can you type here any one solved problem of this type, as given in your book, or by your teacher? Then I can check if I am using the same method as your teacher prefers (but, of course, my solutions are also correct).



here is a problem tht is solved...

If y varies inversely as x, and y=50 when x=3, find y when x =12?

x*y
50*3=12*y
150=12y
y=12.5
akhl thumbnail
18th Anniversary Thumbnail Dazzler Thumbnail Fascinator 1 Thumbnail
Posted: 13 years ago
I edited my solutions to #2 to #7. Now I have used the method in the solved example you posted.
But, if you have already copied the earlier solutions, that is ok because earlier method was also correct.
Now, I am going to answer the remaining problems.

akhl thumbnail
18th Anniversary Thumbnail Dazzler Thumbnail Fascinator 1 Thumbnail
Posted: 13 years ago
@priya_94
8). Suppose z varies directly as w and inversely as uv, and z=5 when u=9, v=4 and w=13. find w when z=10, u=6, and v=151.
Check again. Are you sure you entered all the valus and variable names correctly?

9). The Gravitational force that the earth exerts on an object varies inversely as the square of its distance frm the center of the earth. If the earth exerts a force of 19,000 N on an orbiter module on the earth's surface, 64,00 km frm the center of the earth, what force would it exert on the module when it is 8000 km frm the earth's center.
F * r^2 = constant
19,000 * 6400^2 = F * 8000^2
F = 19,000 * 6400^2 / 8000^2
F = 12,160 N (Answer)

Are you sure the first distance is 64,00 km or is it 64,000 km ?

10). The attractive force between two oppositely charged particles varies jointly with the magnitude of their charges and inversely as the square of the distance between them. the force between two particles with charge of 5 Micro coulombs and 1 micro coulombs, which are 0.3 m apart, is 0.5 N. what is the force between charges of 2 micro coulombs and 6 micro coulombs that are 0.4 m apart.
F/(Q1*Q2) * r^2 = constant
0.5/(5*1) * 0.3^2 = F/(2*6) * 0.4^2
0.009 = F/75
F = 75 * 0.009
F = 0.675 N


11). Suppose z varies jointly as x and y and inversely as w, and z=6 when x =4, y= 5 and w= 8. find z when x=2, y=6 and w=4.
z/(xy) * w = constant
6/(4*5) * 8 = z/(2*6) * 4
2.4 = z/3
z = 2.4 * 3
z = 7.2 (Answer)


12). Suppose z varies directly as w and inversely as uv, and z=10 when u=8, v=6 and w=4. find w when z=16, u=15 and v=3.
(z/w) * uv = constant
(10/4) * 8 * 6 = (16/w) * 15 * 3
120 = 720/w
w = 720/120
w = 6 (Answer)


13). The electrostatic force of repulsion between two apha particles varies inversely as the square of the distance between them. If this force is 0.384 newtons when the particles are 0.05 picometers apart, what is the force when the particles are 0.2 picometers apart.
F/r^2 = constant
0.384/0.05^2 = F/0.2^2
153.6 = F/0.04
F = 153.6 * 0.04
F = 6.144 N

-InnocentSoul- thumbnail
14th Anniversary Thumbnail Sparkler Thumbnail
Posted: 13 years ago
8). Suppose z varies directly as w and inversely as uv, and z=5 when u=9, v=4 and w=12. find w when z=10, u=6, and v=15
-InnocentSoul- thumbnail
14th Anniversary Thumbnail Sparkler Thumbnail
Posted: 13 years ago
9). The Gravitational force that the earth exerts on an object varies inversely as the square of its distance frm the center of the earth. If the earth exerts a force of 19,000 N on an orbiter module on the earth's surface, 64,00 km frm the center of the earth, what force would it exert on the module when it is 8000 km frm the earth's center.
F * r^2 = constant
19,000 * 6400^2 = F * 8000^2
F = 19,000 * 6400^2 / 8000^2
F = 12,160 N (Answer)

Are you sure the first distance is 64,00 km or is it 64,000 km ?

its 64,00
akhl thumbnail
18th Anniversary Thumbnail Dazzler Thumbnail Fascinator 1 Thumbnail
Posted: 13 years ago

Originally posted by: priya_94

8). Suppose z varies directly as w and inversely as uv, and z=5 when u=9, v=4 and w=12. find w when z=10, u=6, and v=15



(z/w) * uv = constant
(5/12) * 9 * 4 = (10/w) * 6 * 15
15 = 900/w
w = 900/15
w = 60 (Answer)


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