B Initial Velocity

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1. Jul 15, 2017

sinchan

Why we take initial velocity of dropped object downwards as 0 and 25m/s when the object is thrown 25m/s upwards ?

What is then initial velocity cause when t=0 both object dropping and moving upwards had 0 velocity - in other words when object came to motion at both places it had some velocity?

2. Jul 15, 2017

Staff: Mentor

Are you saying that, when you throw a ball, its velocity is zero when it leaves your hand? And, when you drop a ball, its velocity isn't zero when it leaves your hand?

3. Jul 15, 2017

sinchan

I can state better when I understand initial velocity - for me when object is dropped from height or thrown with a velocity upwards both of them has velocity zero when it is in hand but both of them have a velocity when it leaves the hand - but then I am not sure when do we measure initial velocity - when it is in hand or when it just started its moion - so when it is in hand for both case initial velocity is 0 and when it started its motion both of them have a velocity - so why we say that initial velocity of object dropped is 0 while 25 m/s when object is thrown upwards as in my example

4. Jul 15, 2017

Staff: Mentor

This is not correct. When you throw something, the velocity of the object just before it leaves your hand is the same as its velocity just after it leaves your hand (>0). And when you drop something, its velocity just before it leaves your hand is the same as its velocity just after it leaves your hand (=0).

5. Jul 19, 2017

Kaneki123

i understand your confusion...When you drop a ball, its velocity increases by every second.It becomes 9.8 m/s 1 second after leaving your hand.However, when you throw a ball, the only reason the ball goes out from your hand is because your provided it with acceleration, which caused it to have a velocity, which started its motion, hence its "initial" velocity. When you dropped the ball, the velocity at which the "downwards" motion of ball started is 0 m/s...
Hope this helps

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