Physics - Mechanics: Applications of Newton's Second Law (12.5 of 20) Corrected Video

In this video I will show you how to calculate the forces needed for a person pull himself up a stationary, moving, and accelerating elevator.

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[srijahnavi]

I have always struggled in these types of problems, thanks a lot for clearing my doubts.

[RobertJohnson-nquy]

Helped me figure out a problem in the Feynman lectures, appreciate it!

[ShimaaMohamed-jfjl]

Thank you very much, we appreciate your effort to help us and explain the information in a simple and wonderful way

[ALAL-jmlr]

hi, i think the trick to understand why T1 is always mg+Mg, even though there is new pulling(grasping) downward
from the person inside elevator is to think as this:
1>idea1: what if the end of rope where person is catching is connected to same elevator .
now total weight is divided between two ropes...and T1=mg+Mg.
2>idea 2: u may say hey..there one end of rope connected to elevator which have pulling force as total weight
which is mg+MG, and there is new pulling force from the guy who catching the other end....
so T1 must be adding mg+Mg+guy pulling wait as this guy pull the rope....his weight mg inside
elevator is reduced: as guy pulling force increase==>mg decrease of same amount....
and so total T1 is keep same as before mg+Mg....
hope this explain it more

[ustka]

Good day Sir,

I don't understand why the school teaches that it is possible to pull yourself with this kind of solution. It takes 3/4 ths of the power to pull oneself with this basket in comparation to pulling yourself up.

[kartikeyrajgupta]

Hello sir I am Indian, your explanation is very clear
Thank you so much sir

[trafalgardyobk]

If person pulls the rope then his wheight will be reduced to 0 and T1=50(9.8)
and
T2 =25(9.8)+[50(9.8)-25(9.8)]

25(9.8):means that wheight of man is transformed to T2 and
[50(9.8)-25(9.8)]:means additional force that the man should add to equal the elevator weight
Is this right?

[devyn]

is this not wrong? In this video it should be.

Static: Fnet = 0
(Force of the box)+T2=0
T2=g(75kg) = T3
T1=T2+T3
= 2g(75kg)

I feel like he forgot which was T1 and rolled with it.

[michaelsilagy]

I'm still a little confused like the others in the comment section on how there is a mechanical advantage to this pulley system.
From my understanding, if you were to hang an object weighing 37.5 kg (367.5N) on the other side instead of applying a pulling force of 367.5 N, the lift on the left side would start to fall, yes? Why does pulling on the rope then create a 2:1 difference in the needed force for there to be no acceleration?

Thanks!

[shoaibqureshi]

Hi sir what if the person leaves the rope then the lift will go free fall but will the man will go up or down after leaving the rope

[dhruvmk]

I have a question.

Let's analyze just the boy and the carrier. There are too forces acting on them - force due to gravity and force tension from the rope. Since they are in static equilibrium, the net force has to be zero. Thus, Tension must be equal to force due to gravity, which is (M+m)g = 735 N.

Why is this wrong? Seems like perfectly logical physics to me.

[ashwina]

sir, if we put a weighing machine of weight 1kg where the man stands will it show the weight of man as 12kg

[nikkireddinikki]

if the lift is moving down with acceleration 1 m/s2

[fatimahrashid]

sir,
in case (A)
shouldnt the total tension be equal to 2*735 N since the the system is stationary and must therefore have equal weights suspended from both the rope sides?
thanks in advance!

[iyadindia]

Any body here how the case 2.25 is different from normal case in which if a mass is suspended over pulley attached with one end of rope over the pulley, to lift the object we have to apply a force equivalent to its weight

Any body here pls make clarification

[scimaniac]

What would happen if the person pulled more than or equal to his body weight?

[nicholaslombardo]

All the answers should be doubled as you could see expecially towards the end of the video he writes the wrong subscript causing all the answers to be scaled down by a factor of two.

[muddassir]

What is the force that the person exert on the lift?

[iyadindia]

My question is this
How its possible to set a body into uniform motion from rest without applying any additional force
Or what makes the rest lift into uniform motion

Pls clarify

[petereziagor]

Haha, one way I understood this problem is to see the whole weight as one.
If the person is not applying the force, the whole system would fall at g and to stop it from falling, the hang has to take up the tension of the whole weight and since it's in a pulley system, the system has to be balanced.
Of course, the person can't apply a force greater than his weight and the tension on the strings pulling on the hang must be equal, pulley system.