Acceleration Graph: Answer 5 Correct?

[Manasan3010]

Homework Statement

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Relevant Equations

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I chose Answer 5 but the given answer was 1. Am I correct or what was the mistake?

 

[Orodruin]

What is your reasoning for choosing 5?

 

[Drakkith]

Answer 5 shows an initial negative acceleration (away from the Earth according to the question) with an instantaneous jump to a positive acceleration. Is that how gravity works?

 

[Manasan3010]

What is your reasoning for choosing 5?

The acceleration towards the Earth ip positive so when we throw the ball in opposite direction acceleration will be negative and this causes the initial velocity to decrease and become zero at some height after the U-turn object travels towards Earth which causes positive acceleration hence the velocity increases.
I think the instantaneous jump to a positive acceleration is caused at the point where object starts to return to the Earth from air.

 

[Orodruin]

The acceleration towards the Earth ip positive so when we throw the ball in opposite direction acceleration will be negative

Why? Does the direction of acceleration depend on the velocity?

Note that acceleration is rekated to the change in velocity, not to the change in speed.

 

[Manasan3010]

Why? Does the direction of acceleration depend on the velocity?

Note that acceleration is related to the change in velocity, not to the change in speed.

Have a look at this link
Please explain me the answer I am so confused :(

 

[archaic]

acceleration is due to a force. which force do you think is acting upon the particle?

 

[Orodruin]

Have a look at this link
Please explain me the answer I am so confused :(

That is not how this forum works. You have been given several hints as to how to think about this problem. It is better for your long time learning to consider those hints and their implications. If you are still confused after that, you need to specify what confuses you and why. You will not be handed the answer on a platter because that is not a good way of learning.

 

[RPinPA]

Let me talk a little in general about velocity and acceleration and what direction changes are in.

You know that $a = \Delta v/\Delta t$. If $\Delta v$ is positive that means $v$ increased. An increase could be going from 0 to 3, or from 2 to 5, or from -1 to +1, or from -5 to -2.

[No, I'm not putting units on these, even though I'm a guy who always complains when students leave units off. The reason is that these remarks are true for any units.]

In particular study those last two examples. The final velocity minus the initial velocity is positive. Those are all changes which go to the right on the number line. Those are situations in which $\Delta v$ is positive. Going from -1 to +1 is an increase in velocity (not in speed, and here is why your instructors make a distinction between speed and velocity). The velocity is getting more positive. It is moving in a positive direction. The acceleration is positive.

In the same way, $\Delta v$ negative means $v$ is getting more negative. So that could be going from +5 to +2. But it could also be going from +1 to -2, or from -2 to -5. Those are all negative accelerations.

Here's one other principle to keep in mind: $F = ma$. That means $a = F/m$. What does that tell you about the relationship between the direction of F and the direction of a? Remember m is always positive.

 

[sojsail]

If you are confused by what is said in any of our posts, likely any of us that are connected could explain/reword the post for you. We don't explain how to get the answer, but if necessary we can explain posts that have come in for you.

 

[sojsail]

The acceleration towards the Earth ip positive so when we throw the ball in opposite direction acceleration will be negative and this causes the initial velocity to decrease and become zero at some height after the U-turn object travels towards Earth which causes positive acceleration hence the velocity increases.
I think the instantaneous jump to a positive acceleration is caused at the point where object starts to return to the Earth from air.

In graphs of a thrown ball, assume that time starts when the ball leaves the hand. So would the acceleration of the throwing motion be part of the graph?

 

[Manasan3010]

Thank You guys I understand now. I think the reason I chose Answer 5 was because I got confused with the direction of motion and I also forget that Gravitational acceleration will be same no matter what the direction of motion is.