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Math Help - Two questions (one just checking formula)

  1. #1
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    Red face Two questions (one just checking formula)

    To solve this question:
    Suppose you deposit $100 in an account that earns 0.5% each month. You make no withdrawals from the account and deposit no more money into the account. How much money will you have in the account after 4 years?

    Do I use A = P(1 + rt) to solve this question? If so, is my answer right:

    A = P(1 + rt)
    A = 100[1 + (.5 x 48)]
    A = 100[1 + 24]
    A = 100[25]
    A = 2500


    Second question: (I don't even know where to begin & I have to show my work!)
    A projectile is fired directly upward with amuzzle velocity of 860 feet per second from a height of 7 feet above the ground.
    a. Determine a function for the height of the projectile "t" seconds after it's released.
    b. How long does it take the projectile to reach a height of 100 feet on its way up?
    c. How long is the projectile in the air?
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  2. #2
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    Quote Originally Posted by chickenwing View Post
    To solve this question:
    Suppose you deposit $100 in an account that earns 0.5% each month. You make no withdrawals from the account and deposit no more money into the account. How much money will you have in the account after 4 years?

    Do I use A = P(1 + rt) to solve this question? If so, is my answer right:

    A = P(1 + rt)
    A = 100[1 + (.5 x 48)]
    A = 100[1 + 24]
    A = 100[25]
    A = 2500
    No the formula is given below.
    Attached Thumbnails Attached Thumbnails Two questions (one just checking formula)-picture9.gif  
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  3. #3
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    Quote Originally Posted by chickenwing View Post
    Second question: (I don't even know where to begin & I have to show my work!)
    A projectile is fired directly upward with amuzzle velocity of 860 feet per second from a height of 7 feet above the ground.
    a. Determine a function for the height of the projectile "t" seconds after it's released.
    b. How long does it take the projectile to reach a height of 100 feet on its way up?
    c. How long is the projectile in the air?
    The standard function is a quadradic:
    s(t)=(-1/2)gtē+vt+h

    v is initial velocity which is 860 feet per second which is going to be positive since it is going up.

    h is initial height which is 7 feet.

    g is the decelleration from gravity. Which is 32 feet per second per second.

    Thus,
    s(t)=-16tē+870t+7
    ~~~
    The obejct reaches 100 feet when s(t)=100 for some value t.
    Thus,
    -16tē+870t+7=100
    Thus,
    -16tē+870t-93=0
    Important. When you solve this using quadradic formula you shall get two values for t. Select the first one because the problem say "..going up...".
    ~~~
    That is equivalent to saying amount of time until it comes down.
    Solve
    s(t)=0 for some positive t value.
    Thus,
    -16tē+870t+7=0
    Apply quadradic formula.
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  4. #4
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    Quote Originally Posted by ThePerfectHacker View Post
    The standard function is a quadradic:
    s(t)=(-1/2)gtē+vt+h

    v is initial velocity which is 860 feet per second which is going to be positive since it is going up.

    h is initial height which is 7 feet.

    g is the decelleration from gravity. Which is 32 feet per second per second.

    Thus,
    s(t)=-16tē+860t+7
    ~~~
    The obejct reaches 100 feet when s(t)=100 for some value t.
    Thus,
    -16tē+860t+7=100
    Thus,
    -16tē+860t-93=0
    Important. When you solve this using quadradic formula you shall get two values for t. Select the first one because the problem say "..going up...".
    ~~~
    That is equivalent to saying amount of time until it comes down.
    Solve
    s(t)=0 for some positive t value.
    Thus,
    -16tē+860t+7=0
    Apply quadradic formula.
    What he said, except with 870 turned into 860.

    -Dan
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