## A Comeback Post (Assignment related)

Discuss Physics and Physics Olympiad related problems here

## What is the acceleration of a vertically thrown object at the peek of its path?

$9.8ms^{-2}$
3
75%
$0ms^{-2}$
1
25%

Asif Hossain
Posts:194
Joined:Sat Jan 02, 2021 9:28 pm
A Comeback Post (Assignment related)
For HSC first year in the first week (surely everybody has submitted that by now) there was a problem stating:
What is the acceleration of a vertically thrown object at the peek of its path?
Somebody say it is $0ms^{-2}$ some say it is $9.8ms^{-2}$
I am on the side of $9.8ms^{-2}$ here is my reason:
At the peek the object is going to be a free falling object so at time $t$ its velocity $v=v_0 +gt$
So, at any moment the acceleration should be $\frac{d}{dt}(v_0 +gt) \Rightarrow g=9.8ms^{-2}$
Hmm..Hammer...Treat everything as nail

Mehrab4226
Posts:230
Joined:Sat Jan 11, 2020 1:38 pm

### Re: A Comeback Post (Assignment related)

I am also on the side of $9.8 ms^{-2}$, because if the acceleration is $0$. Then the object is not supposed to move down. But it does move down. So it has acceleration.
The Mathematician does not study math because it is useful; he studies it because he delights in it, and he delights in it because it is beautiful.
-Henri Poincaré

Anindya Biswas
Posts:264
Joined:Fri Oct 02, 2020 8:51 pm
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### Re: A Comeback Post (Assignment related)

Acceleration is the second derivative of position with respect to time.
The position of the object is given by,
$y(t)=v_0t-\frac12gt^2$
$\Rightarrow y''(t)=-g$

Some confusion is arising that since the object was moving upwards, there should be an upward force acting on that object, and the gravitational force cancelled that force and the total force should be zero.
But the problem is, there was no force acting on that thing upwards. The upward force acted when it was in our hand. As soon as it left the ground, all upward forces stopped acting and the object moved upward for its inertia. So gravitational force never cancelled anything, it was the only force acting there.
"If people do not believe that mathematics is simple, it is only because they do not realize how complicated life is."
John von Neumann

Asif Hossain
Posts:194
Joined:Sat Jan 02, 2021 9:28 pm

### Re: A Comeback Post (Assignment related)

Anindya Biswas wrote:
Fri Jun 25, 2021 8:08 pm
Acceleration is the second derivative of position with respect to time.
The position of the object is given by,
$y(t)=v_0t-\frac12gt^2$
$\Rightarrow y''(t)=-g$

Some confusion is arising that since the object was moving upwards, there should be an upward force acting on that object, and the gravitational force cancelled that force and the total force should be zero.
But the problem is, there was no force acting on that thing upwards. The upward force acted when it was in our hand. As soon as it left the ground, all upward forces stopped acting and the object moved upward for its inertia. So gravitational force never cancelled anything, it was the only force acting there.
-g or g?? Hmm..Hammer...Treat everything as nail

Anindya Biswas
Posts:264
Joined:Fri Oct 02, 2020 8:51 pm
Contact:

### Re: A Comeback Post (Assignment related)

Asif Hossain wrote:
Sat Jun 26, 2021 10:43 pm
Anindya Biswas wrote:
Fri Jun 25, 2021 8:08 pm
Acceleration is the second derivative of position with respect to time.
The position of the object is given by,
$y(t)=v_0t-\frac12gt^2$
$\Rightarrow y''(t)=-g$

Some confusion is arising that since the object was moving upwards, there should be an upward force acting on that object, and the gravitational force cancelled that force and the total force should be zero.
But the problem is, there was no force acting on that thing upwards. The upward force acted when it was in our hand. As soon as it left the ground, all upward forces stopped acting and the object moved upward for its inertia. So gravitational force never cancelled anything, it was the only force acting there.
-g or g?? Well, the position function was upward displacement, so $-g$ is the upward acceleration. That means $g$ is the downward acceleration.
"If people do not believe that mathematics is simple, it is only because they do not realize how complicated life is."
John von Neumann

sakib17442
Posts:15
Joined:Sun Apr 11, 2021 10:04 pm
Contact:

### Re: A Comeback Post (Assignment related)

Oops, sorry I misunderstood this and voted for 0. Please forgive me
Games You can't win because you'll play against yourself.
---Dr.Seuss

celinedion
Posts:1
Joined:Fri Feb 03, 2023 3:17 pm

### Re: A Comeback Post (Assignment related)

Mehrab4226 wrote:
Fri Jun 25, 2021 10:10 am
I am also on the side of 98ms−2, because if the acceleration is 0 . Then the object is not supposed to move down. But it does move down. So it has acceleration.mapquest driving directions
Me too!