Acceleration upwards and the effect of 'g'

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Discussion Overview

The discussion revolves around the interpretation of acceleration in the context of a body moving upwards with a constant acceleration and the effects of gravitational acceleration. Participants explore the application of Newton's laws of motion, particularly in scenarios involving forces acting on objects in motion, such as a lamp in a descending lift.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether the upward acceleration of a body implies that gravitational acceleration must be subtracted from another value, suggesting a misunderstanding of how forces interact.
  • Another participant asserts that a body cannot be accelerating upwards while simultaneously experiencing gravitational acceleration in the opposite direction, indicating a potential confusion about the net forces involved.
  • A participant emphasizes the importance of drawing a free body diagram to analyze the forces acting on the lamp in the elevator scenario.
  • There is a clarification regarding a numerical error in the initial post, correcting the value from 25 to 2.
  • One participant explains that the net force acting on a body moving upwards is the result of both the gravitational force and the force propelling the body upward, highlighting the role of gravity in determining net acceleration.

Areas of Agreement / Disagreement

Participants express differing views on the role of gravitational acceleration in the context of upward motion and the application of Newton's laws. There is no consensus on how to approach the relationship between upward acceleration and gravitational force.

Contextual Notes

Participants do not fully resolve the implications of combining gravitational acceleration with other forms of acceleration in their discussions, leaving some assumptions and definitions unaddressed.

Xenoned
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Hi,

If a statement something like this is given:
"A body is going up with a constant acceleration of 2 m/s^2"

Does it mean that acceleration due to gravity acts on it and we have to subtract 9.8 from 25?

We subtract forces by Newton's laws of motion right?

There is a question like this:
"A lamp hangs vertically from a chord in a descending lift. The lift has a deceleration of 5.2 m/s2 before coming to a halt. If the tension in cord is 30 N, find the mass of the lamp."

We answer it by T=m(g+a) ; a= acceleration/deceleration and get the answer.
but here we use g+a .

why not just acceleration?
Why shouldn't we subtract or add g in case of 1D motion?
 
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Where do you get 25 from?

If a body is accelerating upward at 2 m/s^2, it cannot at the same time be accelerating at 9.8 m/s^2 in the opposite direction.

In the elevator question, you should draw a free body diagram of the lamp and the cord to determine all of the forces acting on the lamp while the elevator is coming to a stop.
 
Xenoned said:
Hi,

If a statement something like this is given:
"A body is going up with a constant acceleration of 2 m/s^2"

Does it mean that acceleration due to gravity acts on it and we have to subtract 9.8 from 25?

We subtract forces by Newton's laws of motion right?

There is a question like this:
"A lamp hangs vertically from a chord in a descending lift. The lift has a deceleration of 5.2 m/s2 before coming to a halt. If the tension in cord is 30 N, find the mass of the lamp."

We answer it by T=m(g+a) ; a= acceleration/deceleration and get the answer.
but here we use g+a .

why not just acceleration?
Why shouldn't we subtract or add g in case of 1D motion?
Those are two contradictory questions! You ask why we use g at all in the first question then ask why we shouldn't use it in the second question!
 
I am sorry. It's not 25 but 2.
 
Xenoned said:
Hi,

If a statement something like this is given:
"A body is going up with a constant acceleration of 2 m/s^2"

Does it mean that acceleration due to gravity acts on it and we have to subtract 9.8 from 25?

The force of gravity acts on it. The net force on the body produces the given acceleration of 2 m/s2 upwards. The net force is comprised of the gravitational force and the force exerted by whatever mechanism is propelling the body upward.
 

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