Why does the g (acceleration) go in the opposite direction?

Watch
username2199397
Badges: 18
Rep:
?
#1
Report Thread starter 2 years ago
#1
https://www.youtube.com/watch?v=uP7RBWsoQ44
4:31 of the video
0
reply
username2199397
Badges: 18
Rep:
?
#2
Report Thread starter 2 years ago
#2
OH is it because by the time the particle q moves up, it will be under the influence of gravity as the velocity will be 0 mid air?
0
reply
RDKGames
Badges: 20
Rep:
?
#3
Report 2 years ago
#3
(Original post by shohaib712)
OH is it because by the time the particle q moves up, it will be under the influence of gravity as the velocity will be 0 mid air?
Gravity is ALWAYS acting down. If you choose upwards to be +ve then your gravity acceleration is always -ve.

Until P reaches the ground, Q is accelerating upwards with a +ve acceleration that satisfies 2a = T-2g.

When P reaches the ground, the string becomes slack since there's nothing to drag the string down anymore, hence tension becomes 0. For Q this means there is no more tension acting up and only the one force is acting down, namely the gravitational force. SO in this process of motion, you get that 2a = 0-2g \implies a = -g for it.
0
reply
username2199397
Badges: 18
Rep:
?
#4
Report Thread starter 2 years ago
#4
(Original post by RDKGames)
Gravity is ALWAYS acting down. If you choose upwards to be +ve then your gravity acceleration is always -ve.

Until P reaches the ground, Q is accelerating upwards with a +ve acceleration that satisfies 2a = T-2g.

When P reaches the ground, the string becomes slack since there's nothing to drag the string down anymore, hence tension becomes 0. For Q this means there is no more tension acting up and only the one force is acting down, namely the gravitational force. SO in this process of motion, you get that 2a = 0-2g \implies a = -g for it.
Oh i see so the same would apply for (lets say q had a mass of 4kg) then if the string became slack on p, then there would be no tension on q so its resultant force would be: 4a=0-4g and we would still get get a = -g. So bassically the reason why gravity is the only force acting on the particle is because the string has no tension as it isnt taut aymore?
0
reply
username2199397
Badges: 18
Rep:
?
#5
Report Thread starter 2 years ago
#5
(Original post by RDKGames)
Gravity is ALWAYS acting down. If you choose upwards to be +ve then your gravity acceleration is always -ve.

Until P reaches the ground, Q is accelerating upwards with a +ve acceleration that satisfies 2a = T-2g.

When P reaches the ground, the string becomes slack since there's nothing to drag the string down anymore, hence tension becomes 0. For Q this means there is no more tension acting up and only the one force is acting down, namely the gravitational force. SO in this process of motion, you get that 2a = 0-2g \implies a = -g for it.
in the last question in this video:
https://www.youtube.com/watch?v=SGEscXwQUFw

Why does he make F=2T? Shouldnt the pully also be affected by the mass of the particles and doesnt the T cancel out as they are affecting the string in opposite directions?
0
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
Back
to top
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise

Have you experienced financial difficulties as a student due to Covid-19?

Yes, I have really struggled financially (17)
13.08%
I have experienced some financial difficulties (31)
23.85%
I haven't experienced any financial difficulties and things have stayed the same (58)
44.62%
I have had better financial opportunities as a result of the pandemic (20)
15.38%
I've had another experience (let us know in the thread!) (4)
3.08%

Watched Threads

View All
Latest
My Feed