# Two questions (one just checking formula)

• Oct 4th 2006, 11:06 AM
chickenwing
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?
• Oct 4th 2006, 12:10 PM
ThePerfectHacker
Quote:

Originally Posted by chickenwing
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.
• Oct 4th 2006, 12:31 PM
ThePerfectHacker
Quote:

Originally Posted by chickenwing
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?

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
• Oct 4th 2006, 03:39 PM
topsquark
Quote:

Originally Posted by ThePerfectHacker
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

What he said, except with 870 turned into 860. :)

-Dan