Free Falling Objects: Find Initial Velocity of Q

In summary, the first stone falls 19.6m and the second stone is released from a cliff of height 122.5m above the ground. The second stone falls a shorter distance but reaches the ground at the same time as the first stone.
  • #1
stupif
99
1
1. stone p is releasedfrom a cliff of height 122.5m above the ground. after falling a distance of 19.6m, another stone Q is lauched straight downward.if given that p and Q reached the ground same time, find the initial velocity of Q( answer :26.1m/s

i using s=ut +1/2a[t][2] to find out the t, t= 5s
time of p=time of Q
i using s=ut +1/2a[t][2] to find out the initial velocity of u by change the S.
my answer is -3.92m/s
 
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  • #2
Hi stupif. You're using the correct equations and your figure of 5 seconds is correct for the time of flight of the first stone.

The key to getting the correct answer is to figure out the correct time of flight for the second stone. So tell us what number you're using for this quantity and how you arrived at it.
 
  • #3
then i used 122.5m - 19.6m=102.9m, so i using 102.9m as stoneQ's distance
 
  • #4
stupif said:
then i used 122.5m - 19.6m=102.9m, so i using 102.9m as stoneQ's distance
No you're interpreting the question incorrectly. The second stone is released from the same height as the first one (that is, 122.5m). This means that the second stone falls the same distance but does so in a shorter time period. If you work out what this shorter time period is then you can easily work out the required initial velocity. (the books answer is correct btw).
 
  • #5
then s= same, t=same, a=same, just u is variable. how to calculate??
 
  • #6
No, "t" is NOT the same. The second stone is released AFTER the first stone has already fallen 19.6m, yet they arrive at the ground at the same time! So the time of flight of the second stone MUST be smaller. So that's the key to the problem, find the time of flight for the second stone and then you can easily find "u".

How long does it take for the first stone to fall 19.6m?

Use the above to find the time of flight for the second stone.
 
  • #7
thank you...i got it...
 

Related to Free Falling Objects: Find Initial Velocity of Q

1. What is a free falling object?

A free falling object is an object that is falling under the sole influence of gravity and no other forces, such as air resistance or external forces.

2. How do you find the initial velocity of a free falling object?

To find the initial velocity of a free falling object, you need to use the equation v = u + at, where v is the final velocity, u is the initial velocity, a is the acceleration due to gravity (9.8 m/s²), and t is the time the object has been falling. Rearranging the equation, we get u = v - at.

3. What is the acceleration of a free falling object?

The acceleration of a free falling object is the acceleration due to gravity, which is approximately 9.8 m/s². This means that every second, the object's velocity increases by 9.8 meters per second.

4. Can the initial velocity of a free falling object be negative?

Yes, the initial velocity of a free falling object can be negative. This means that the object was thrown or dropped downwards with a velocity in the negative direction (opposite to the direction of gravity).

5. How does air resistance affect the initial velocity of a free falling object?

Air resistance can affect the initial velocity of a free falling object by slowing it down. Air resistance is a force that opposes the motion of an object through the air, and it increases with velocity. This means that the faster an object falls, the more air resistance it experiences, and the slower its initial velocity will be.

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