Acceleration or Velocity?

• bonkysleuth

  4 Dec 07, 18:37

  A mass of 2.5kg falls from rest. Which of the following statements is correct?
  
  -Falls with constant velocity of 2.5 m/s
  -Falls with constant velocity of 10 m/s
  -Falls with constant acceleration of 2.5 m/s2
  -Falls with constant acceleration of 10m/s2
  
  Kindly justify your answer by explaining it to me. I'm such a noob that I do not understand such stuffs. Haha.
  
  thanks.
• the Bear

  4 Dec 07, 18:39

  falls with constant acceleration of 10m/s2
  
  because that is the law of gravity...
• Hello Kitty

  4 Dec 07, 18:39

  Homework Forum
• Daisuke-kun

  4 Dec 07, 18:40

  ummm..
  i just noe that a BAM song will b heard.
• Darkness_hacker99

  4 Dec 07, 18:40

  Fall with constant acceleration 10m/s2 due to gravitational pull.
• bonkysleuth

  4 Dec 07, 18:42

  Originally posted by the Bear:

  falls with constant acceleration of 10m/s2
  
  because that is the law of gravity...

  Thanks. But why can't velocity be constant? If you say it falls with constant acceleration of 10m/s2, then it means that the object keeps accelerating when falling?
• the Bear

  4 Dec 07, 18:45

  yes.. that's only true in a vacuum..
  
  if it falls in at atmosphere, there will be resistance due to the air..
  
  the faster it falls, the more force due to the resistance until the force from the resistance equates the force pulling the object (gravity)
  
  the object then falls at constant speed.. this is called terminal velocity..
  
  

  Originally posted by bonkysleuth:

  Thanks. But why can't velocity be constant? If you say it falls with constant acceleration of 10m/s2, then it means that the object keeps accelerating when falling?

• MyPillowTalks

  4 Dec 07, 18:51

  10m/s
  
  earth's gravitational pull is 9.8, ~ 10
• bonkysleuth

  4 Dec 07, 18:52

  Originally posted by the Bear:

  yes.. that's only true in a vacuum..
  
  if it falls in at atmosphere, there will be resistance due to the air..
  
  the faster it falls, the more force due to the resistance until the force from the resistance equates the force pulling the object (gravity)
  
  the object then falls at constant speed.. this is called terminal velocity..
  
  

  So anything that falls will accelerate with the same acceleration/ force due to gravity??? So what is the difference between velocity and speed?
• ohnoez!

  4 Dec 07, 18:55

  Originally posted by bonkysleuth:

  So anything that falls will accelerate with the same acceleration/ force due to gravity??? So what is the difference between velocity and speed?

  speed is scalar(dont need care bout direction), velocity is vector(need care)
• bonkysleuth

  4 Dec 07, 18:58

  Originally posted by the Bear:

  yes.. that's only true in a vacuum..
  
  if it falls in at atmosphere, there will be resistance due to the air..
  
  the faster it falls, the more force due to the resistance until the force from the resistance equates the force pulling the object (gravity)
  
  the object then falls at constant speed.. this is called terminal velocity..
  
  

  And to quote you again, you mentioned that resistance builds up over time with increased speed. So since resistance becomes heavier, then acceleration will be reduced to an amount lesser than 10m/s2 right?
• annoy-you-must

  4 Dec 07, 18:58

  Originally posted by bonkysleuth:

  A mass of 2.5kg falls from rest. Which of the following statements is correct?
  
  -Falls with constant velocity of 2.5 m/s
  -Falls with constant velocity of 10 m/s
  -Falls with constant acceleration of 2.5 m/s2
  -Falls with constant acceleration of 10m/s2
  
  Kindly justify your answer by explaining it to me. I'm such a noob that I do not understand such stuffs. Haha.
  
  thanks.

  Under the influence of a gravitational field, any falling object will undergo acceleration.
  
  Therefore, option one and two is obviously out. If something undergo acceleration, it cannot have a constant velocity.
  
  The gravitational field strength of planet Earth is approximately 10N/kg (memorise). Therefore, using the derived formulae from the Newton's Second Law, 'F=ma', where F is the weight of the object (W=mg=10*2.5) (since weight is the only force acting on the object, ignoring the effect of air resistance obviously), we get a=F/m= (10*2.5)/2.5=10m/s^2.
• annoy-you-must

  4 Dec 07, 19:00

  Originally posted by bonkysleuth:

  And to quote you again, you mentioned that resistance builds up over time with increased speed. So since resistance becomes heavier, then acceleration will be reduced to an amount lesser than 10m/s2 right?

  By right, acceleration will decrease over time due to building up of resistance. If the falling distance is long enough, this acceleration will eventually reach zero and the falling object will have a constant final velocity, called terminal velocity.
  
  However, some questions may require the student to ignore the effect of air resistance so as to simplify the calculation. In this question, you can just ignore air resistance.
• N00bism

  31 Dec 07, 10:26

  Originally posted by bonkysleuth:

  A mass of 2.5kg falls from rest. Which of the following statements is correct?
  
  -Falls with constant velocity of 2.5 m/s
  -Falls with constant velocity of 10 m/s
  -Falls with constant acceleration of 2.5 m/s2
  -Falls with constant acceleration of 10m/s2
  
  Kindly justify your answer by explaining it to me. I'm such a noob that I do not understand such stuffs. Haha.
  
  thanks.

  If gravity is constant velocity of 2.5m/s... You jump from 100 storey building, 1hr later your only fall up to 40 storey?
• DrAlienology

  1 Jan 08, 14:43

  Originally posted by N00bism:

  If gravity is constant velocity of 2.5m/s... You jump from 100 storey building, 1hr later your only fall up to 40 storey?

  isn't gravity a form of acceleration?