Why is initial velocity confusing during free fall?

In summary: If a ball is released, then there is some initial velocity, but it's usually small. Usually, when someone is calculating the initial velocity, they would just put 0 for the initial velocity because it doesn't really make a difference.
  • #1
moomoocow
14
0
initial velocity confusion! please help!

hello all,
i am slightly confused about initial velocity during free fall
if a ball is being thrown in the air, and the velocity time graph shows 20m/s at 0 seconds, and -20m/s at 4 seconds, which is when the ball drops
if i want to calculate the displacement, i know that i can use the formula d=(vo)(t) +0.5(a)(t^2)
with vo being initial velocity
why is it that i would have to put 0 for vo? why isn't it 20m/s?
 
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  • #2
Which displacement are you talking about? (I'm assuming that the ball is thrown vertically)
 
  • #3
I'm not sure I understand your question. If a ball is thrown with initial velocity of 20 m/s, then that's your initial velocity. The V0 just means velocity at t=0. If a ball is dropped or released then its V0 is 0.
 
  • #4
the ball is thrown vertically, displacement being the change in distance. oksanav: why is it that If a ball is dropped or released then its V0 is 0?, but then why would the v-t graph show 20m/s at 0 seconds?
 
  • #5
When the ball's thrown initially, it has a velocity of 20 m/s, but as it reaches the top, its velocity goes to zero. After that, its velocity increases, now pointing down, reaching 20m/s just before hitting the ground. Depending on which part you're calculating, you're initial velocity will change.
 
  • #6
moomoocow said:
the ball is thrown vertically, displacement being the change in distance. oksanav: why is it that If a ball is dropped or released then its V0 is 0?, but then why would the v-t graph show 20m/s at 0 seconds?

If a ball is dropped, there usually is no initial velocity, but there can be some. But in that case, it is a throw. It's all about directions.
 

FAQ: Why is initial velocity confusing during free fall?

What is initial velocity confusion?

Initial velocity confusion refers to the misunderstanding or incorrect interpretation of the initial velocity of an object in motion. It is often a result of not properly defining or calculating the initial velocity, which can lead to errors in predicting the motion of the object.

How is initial velocity calculated?

Initial velocity is calculated as the rate of change of an object's position at the start of its motion. It can be calculated by dividing the change in position by the change in time, or by using the formula v0 = (xf - x0) / t, where v0 is the initial velocity, xf is the final position, x0 is the initial position, and t is the time interval.

What are some common mistakes when determining initial velocity?

Some common mistakes when determining initial velocity include not specifying the direction of the velocity, using the final position instead of the initial position, and not accounting for any external forces acting on the object. It is important to carefully define and understand the initial conditions of an object's motion in order to accurately calculate its initial velocity.

How does initial velocity affect an object's motion?

Initial velocity is a crucial factor in determining an object's motion. It determines the direction and speed of the object's motion at the start, and can also impact its acceleration and displacement over time. A higher initial velocity will result in a greater rate of change in position and a longer distance traveled, while a lower initial velocity will result in a slower rate of change and a shorter distance traveled.

What are some real-life examples of initial velocity confusion?

One common example of initial velocity confusion is in sports such as baseball or tennis, where the initial velocity of a ball thrown or hit can greatly affect its trajectory and landing point. Another example is in car accidents, where the initial velocity of the vehicles involved can determine the severity of the collision and the resulting damage. Initial velocity confusion can also occur in physics experiments or simulations, where incorrect initial conditions can lead to inaccurate results.

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