<< Chapter < Page Chapter >> Page >

A ball is dropped from the balcony of a tall building. The balcony is 15 m above the ground. Assuming gravitational acceleration is 9,8 m · s - 2 , find:

  1. the time required for the ball to hit the ground, and
  2. the velocity with which it hits the ground.
  1. It always helps to understand the problem if we draw a picture like the one below:

  2. We have these quantities:

    Δ x = 15 m v i = 0 m · s - 1 g = 9 , 8 m · s - 2
  3. Since the ball is falling, we choose down as positive. This means that the values for v i , Δ x and a will be positive.

  4. We can use [link] to find the time: Δ x = v i t + 1 2 g t 2

  5. Δ x = v i t + 1 2 g t 2 15 = ( 0 ) t + 1 2 ( 9 , 8 ) ( t ) 2 15 = 4 , 9 t 2 t 2 = 3 , 0612 . . . t = 1 , 7496 . . . t = 1 , 75 s
  6. Using [link] to find v f :

    v f = v i + g t v f = 0 + ( 9 , 8 ) ( 1 , 7496 . . . ) v f = 17 , 1464 . . .

    Remember to add the direction: v f = 17,15 m · s - 1 downwards.

By now you should have seen that free fall motion is just a special case of motion with constant acceleration, and we use the same equations as before. The only difference is that the value for the acceleration, a , is always equal to the value of gravitational acceleration, g . In the equations of motion we can replace a with g .

Gravitational acceleration

  1. A brick falls from the top of a 5 m high building. Calculate the velocity with which the brick reaches the ground. How long does it take the brick to reach the ground?
  2. A stone is dropped from a window. It takes the stone 1,5 s to reach the ground. How high above the ground is the window?
  3. An apple falls from a tree from a height of 1,8 m . What is the velocity of the apple when it reaches the ground?

Potential energy

The potential energy of an object is generally defined as the energy an object has because of its position relative to other objects that it interacts with. There are different kinds of potential energy such as gravitional potential energy, chemical potential energy, electrical potential energy, to name a few. In this section we will be looking at gravitational potential energy.

Potential energy

Potential energy is the energy an object has due to its position or state.

Gravitational potential energy is the energy of an object due to its position above the surface of the Earth. The symbol P E is used to refer to gravitational potential energy. You will often find that the words potential energy are used where gravitational potential energy is meant. We can define potential energy (or gravitational potential energy, if you like) as:

P E = m g h

where PE = potential energy measured in joules (J)

m = mass of the object (measured in kg)

g = gravitational acceleration ( 9,8 m · s - 2 )

h = perpendicular height from the reference point (measured in m)

A suitcase, with a mass of 1 kg , is placed at the top of a 2 m high cupboard. By lifting the suitcase against the force of gravity, we give the suitcase potential energy. This potential energy can be calculated using [link] .

Questions & Answers

a perfect square v²+2v+_
Dearan Reply
kkk nice
Abdirahman Reply
algebra 2 Inequalities:If equation 2 = 0 it is an open set?
Kim Reply
y=10×
Embra Reply
if |A| not equal to 0 and order of A is n prove that adj (adj A = |A|
Nancy Reply
rolling four fair dice and getting an even number an all four dice
ramon Reply
Kristine 2*2*2=8
Bridget Reply
Differences Between Laspeyres and Paasche Indices
Emedobi Reply
No. 7x -4y is simplified from 4x + (3y + 3x) -7y
Mary Reply
is it 3×y ?
Joan Reply
J, combine like terms 7x-4y
Bridget Reply
im not good at math so would this help me
Rachael Reply
how did I we'll learn this
Noor Reply
f(x)= 2|x+5| find f(-6)
Prince Reply
f(n)= 2n + 1
Samantha Reply
Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
Crystal Reply
. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
Chris Reply
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
can nanotechnology change the direction of the face of the world
Prasenjit Reply
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
Ali Reply
the Beer law works very well for dilute solutions but fails for very high concentrations. why?
bamidele Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
Got questions? Join the online conversation and get instant answers!
QuizOver.com Reply

Get the best Algebra and trigonometry course in your pocket!





Source:  OpenStax, Maths test. OpenStax CNX. Feb 09, 2011 Download for free at http://cnx.org/content/col11236/1.2
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Maths test' conversation and receive update notifications?

Ask