Question

A bird sitting 16 feet above the ground in an apple tree dislodges an apple. After how many seconds does the apple land on the ground? (Assume no branches interfere with its fall.)

Answer 1

Do you know The first equation of motion ?

Answer 2

@Chrisgoblin there?

Answer 3

yea and no

Answer 4

Anyway make sure that 1 foot = 0.3 m

Answer 5

Well.. we got to find time
=> time t = ?
Distance/ displacement has been given = s = 16 foot = 16*.3 = 4.8m
And acceleration due to gravity = 9.8 m/s^2 = a

We do not have the final velocity ' v '

So, we would be using second equation of motion

which is
\[s = ut + \frac{ 1 }{ 2 }at ^{2}\]

Answer 6

And note that when an object starts to fall the initial velocity i.e. u is taken to be 0

Answer 7

So, plug in the values of all the known elements

Answer 8

im lost...

Answer 9

I am trying to base this off what my book is saying and this is what I got
-4t^2+vt+s

Answer 10

What does your book say ??
So, that I can explain you the way it wants you to understand

Answer 11

The books example doesn't explain much - A window washer drops a wet sponge from a height of 64 feet. After how many seconds does the sponge land on the ground?
Use the vertical motion model to write an equation for the height h (in feet) of the sponge as a function of the time t (in seconds) after it is dropped

Answer 12

Alright, so you are supposed to solve it using equations of motion :)

Answer 13

h=-16t^2+vt+s
0=-16t^2 +(0)t+64
0=-16(t^2-4)
0=-16(t-2)(t+2)
t-2=0 or t+2=0
t=2 or t=-2
The sponge lands on the ground 2 seconds after it dropped.

Answer 14

Ok..!

Answer 15

how did the book come up with that answer?

Answer 16

\(t^2 -4\) = (t-2)(t+2)

The book used (a-b) ( a + b) = \(a^2 - b^2\) identity.

Answer 17

The vertical motion formula is used in many mathematical problems. The formula is h=-16t^+vt+s. H is the final height, T is time, V is velocity, and S is starting height.

(ask.com)

Answer 18

And so, -16(t-2)(t+2) = 0

16 is constant, so, it can not be zero.

t - 2 and t + 2 can be zero.

for t-2 = 0

t = 2

for t + 2 = 0

t = - 2

t can never be negative

so, t = 2

Answer 19

Why don't you, simply plug in the values in the formula
h=-16t^2+vt+s. ?

Answer 20

because I don't know how to do that

Answer 21

Alright!
So listen h = Final Height = It's on the ground now and came there after traveling 16 foot.... so what can it be ?

Don't we have that ?
S = Starting height.. what was it ?
V = velocity with which the object starts it's motion....And as I already told you that an object falling downwards is said to have a velocity of 0m/s when it starts ,...so V = 0

Answer 22

Can you now locate the values of these .. ?

And don't worry, I'm here if any problem comes..:)

Answer 23

0=-16t^2+(0)+16
?

Answer 24

You figured that out !!
Already!
And that's correct.. :)

Answer 25

thanks for the help

Answer 26

You are welcome..!
And just cos of your question, I learnt a new concept...:)

Answer 27

Thanks to you too :)