Deacceleration causes object to move backwards?

[inuka00123]

a imaginary vehicle that travels vertically is deaccelerating at the rate of 5ms/s in upward direction. I understand that when the vehicle is accelerating upwards, at the rate of 5ms/s, the weight of the people inside the vehicle increases, respect to the newtons third law, peoples have a opposite force to the acceleration of the vehicle plus the gravity. but when a vehicle is deaccelerating to the same direction, (vehicle travels vertically) according to the text books the weight decreases, I can't understand if the vehicle is travelling to the same upward direction away from the center of the earth, how the weight decreases, if it does deacceleration must mean it travels back to earth.

 

[gmax137]

If you are traveling in a car or a train that suddenly begins to slow down, are you pressed into your seat, or thrown forward?

 

[jedishrfu]

No it just means the velocity is decreasing as it moves upward.

Imagine a rocket traveling upward thats runs out of fuel it continues upward and depending on its speed and the force of gravity slows down as it moves forward and then begins to fall back to earth.

 

[A.T.]

a imaginary vehicle that travels vertically ...

Downwards or upwards?

... is deaccelerating at the rate of 5ms/s in upward direction.

What is "deaccelerating in upward direction" supposed to mean? There is no vector quantity called 'deacceleration', just acceleration. "Deaccelerating" means that the magnitude of velocity decreses, but that is a scalar quantity and has no direction.

 

[berkeman]

deaccelerating at the rate of 5ms/s

FYI, you have written the units of acceleration (or deceleration) incorrectly.

More correct: 5m/s^2

Better: 5m/(s^2)

Best (using LaTeX): $5\frac{m}{s^2}$

I will send you a DM with tips for posting math at PF using LaTeX (see the "LaTeX Guide" link below the Edit window).

 

[Lnewqban]

... I can't understand if the vehicle is travelling to the same upward direction away from the center of the earth, how the weight decreases, if it does deacceleration must mean it travels back to earth.

You can feel the variation of your weight in a regular elevator:
Static or moving at constant velocity (up or down) = Your feet feel your normal weight.
Accelerating upwards = Your feet feel a greater than normal weight.
Breaking just before reaching the upper floor = Your feet feel a lesser than normal weight until the cabin stops.

 

[A.T.]

You can feel the variation of your weight in a regular elevator:

In modern elevators you barely feel anything, despite getting much quicker to a given floor than in the past. They seem to optimize the acceleration profile by distributing it throughout the entire travel distance, to keep acceleration and jerk below perceptable levels.

 

[Baluncore]

Imagine standing on spring scales in a lift. You will be subjected to Earth's gravity of about, g ≈ 10 m/s². While the lift is not accelerating relative to the building, the scales will show your weight to be 100% of normal.

While the lift accelerates upwards at 5 m/s², you will be subjected to an acceleration of, g + 5 m/s² = 15 m/s², so your weigh on the scales will be 150%, = 50% more than normal.

While the lift accelerates downwards at 5 m/s², you will be subjected to an acceleration of, g - 5 m/s² = 5 m/s², so your weight on the scales will be just 50% of normal.

 

[inuka00123]

If you are traveling in a car or a train that suddenly begins to slow down, are you pressed into your seat, or thrown forward?

I will be thrown forward, the minus acceleration can be thought as slowing down, but I can not understand how slowing down affect my weight, like in a elevator, slowing down causes weight to be less.

 

[A.T.]

I will be thrown forward, the minus acceleration can be thought as slowing down, but I can not understand how slowing down affect my weight, like in a elevator, slowing down causes weight to be less.

It's the same thing:
Car moving forward & slowing down -> acceleration backward -> you are thrown forward
Elevator moving up & slowing down -> acceleration downward -> you are thrown upward

 

[inuka00123]

It's the same thing:
Car moving forward & slowing down -> acceleration backward -> you are thrown forward
Elevator moving up & slowing down -> acceleration downward -> you are thrown upward

did not thought about that, thank you.