Don't Hate Me. More Physics

BMWPower06 · 05-30-2007, 10:58 PM

Ok im a real dumbass when it comes to this shit, yet it seems to come naturally for most of the members on here.

Problem 1:
A window washer pulls herself upward using the bucket-pulley apparatus shown in figure below.

How hard must she pull downward to raise herself slowly at constant speed? The mass of the person plus the bucket is 65.2 kg.

And, if she increases this force by 10.4 percent, what will her acceleration be?

Problem 2:
A 3.15 kg block is pushed along the ceiling with a constant applied force of F = 87.4 N that acts at an angle of alpha = 58.9° with the horizontal, as seen in the figure below.

The block accelerates to the right at 5.49 m/s2. Determine the coefficient of kinetic friction between block and ceiling.

TIA guys

Fartpimpson · 05-30-2007, 11:02 PM

BMWPower06 · 05-30-2007, 11:04 PM

Quote:

Originally Posted by Fartpimpson

BMWPower06 · 05-31-2007, 01:06 AM

bump. where are all the physics guys tonite?

Driv3r · 05-31-2007, 01:14 AM

hahaha out drinking

come back in an hour or twwo and they might show up

Ray · 05-31-2007, 01:26 AM

Sorry I don't have your answer but this may help:

Problem 1
force = mass x acceleration
Since speed is constant, acceleration will be gravity.
Since acceleration is gravity, the force is justified by the weight
force = 65.2 kg (9.8 m/s2)

at 10.4% more force:
just find acceleration if force is increased by 10.4%
acceleration = force(10.4%)/65.2

Ray · 05-31-2007, 01:28 AM

Quote:

Originally Posted by Driv3r

hahaha out drinking

come back in an hour or twwo and they might show up

My 5th Heiny is preventing me from making any sense out of the 2nd prob.

BMWPower06 · 05-31-2007, 02:26 AM

Quote:

Originally Posted by ThreeThirtyEye

Sorry I don't have your answer but this may help:

Problem 1
force = mass x acceleration
Since speed is constant, acceleration will be gravity.
Since acceleration is gravity, the force is justified by the weight
force = 65.2 kg (9.8 m/s2)

at 10.4% more force:
just find acceleration if force is increased by 10.4%
acceleration = force(10.4%)/65.2

i tried doing 65.2*9.8 but it said that was the incorrect answer.

For part 2: whats the force that i use?

BMWPower06 · 05-31-2007, 03:07 AM

Im out for the night, if any1 comes up with the answer please post

Coldintake · 05-31-2007, 04:22 AM

Quote:

Originally Posted by BMWPower06

i tried doing 65.2*9.8 but it said that was the incorrect answer.

For part 2: whats the force that i use?

Non conservative and conservative forces

Josh49 · 05-31-2007, 08:15 AM

I'm at work and the pictures are not working for some reason... In any case, for the first one, are there pulleys involved? If so, you need to include the mechanical advantage that you gain by including pulleys in the system.. I think that is the link you are missing..

hks786 · 05-31-2007, 10:35 AM

Basically she has to overcome her true weight which is 65.2kg x 9.8m/s^2
and also note that the speed is constant so there is NO acceleration in the first part of this question.
Therefore answer is:

F = ma
= 65.2 x 9.8
= 638.96N downwards. (this is the force she needs to pull the rope at)

By increasing the force by 10.4% we achieve a force of 705.41N downwards (by calculation). Then:

a = F/m
= 705.41/65.2
= 10.8 m/s^2

But you said this gave the wrong answer. Hmm, I’m not sure but I would think it is the right answer. She has to overcome her true weight (mass x gravitational force) to get a constant upwards speed. A constant upwards speed also means there is NO acceleration. Then you just have to calculate 10.4% of your answer from part 1 and then add it to the answer from part 1, this will give you the total force. Then just use a = F/m to calculate the acceleration. That is what I would do, but you said it’s wrong…

05-30-2007, 10:58 PM	#1
BMWPower06 A^M=G is nothing w/o the Power of ///M 171 Rep 1,816 Posts Drives: ///M5 & ///M3 Join Date: Jan 2007 Location: Washington D.C. iTrader: (0)	Don't Hate Me. More Physics Ok im a real dumbass when it comes to this shit, yet it seems to come naturally for most of the members on here. Problem 1: A window washer pulls herself upward using the bucket-pulley apparatus shown in figure below. How hard must she pull downward to raise herself slowly at constant speed? The mass of the person plus the bucket is 65.2 kg. And, if she increases this force by 10.4 percent, what will her acceleration be? Problem 2: A 3.15 kg block is pushed along the ceiling with a constant applied force of F = 87.4 N that acts at an angle of alpha = 58.9° with the horizontal, as seen in the figure below. The block accelerates to the right at 5.49 m/s2. Determine the coefficient of kinetic friction between block and ceiling. TIA guys __________________ Indianapolis Red BMW ///M5
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05-30-2007, 11:02 PM	#2
Fartpimpson Colonel 292 Rep 2,414 Posts Drives: E92 335i Join Date: Dec 2006 Location: Alhambra, CA iTrader: (0) Garage List 2007 E92 335i [0.00]
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05-31-2007, 01:06 AM	#4
BMWPower06 A^M=G is nothing w/o the Power of ///M 171 Rep 1,816 Posts Drives: ///M5 & ///M3 Join Date: Jan 2007 Location: Washington D.C. iTrader: (0)	bump. where are all the physics guys tonite? __________________ Indianapolis Red BMW ///M5
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05-31-2007, 01:14 AM	#5
Driv3r Colonel 177 Rep 2,355 Posts Drives: 2006 E46 M3 ZCP Join Date: May 2005 Location: Miami Beach, FL iTrader: (8) Garage List 2006 325i [0.00]	hahaha out drinking come back in an hour or twwo and they might show up __________________ 2006 E46 M3 ZCP 6SPD-Interlagos Blue - 6SPD - SSK - AA Headers -AA Tune - Navigation w/ Splashscreen Mod - 3M Crystalline Series 60 - Carbon Splitters - Swissvax Treated - Bridgestone 2012 Yamaha FZ8 - Matte Black/Grey - Michelin Pilot Pure 2CT - Vortex Rear Sets - Yoshimura R-77D & Fender Delete - Spectro Race Oil - GP Reverse Shifting
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05-31-2007, 01:26 AM	#6
Ray Member 306 Rep 22,825 Posts Drives: three series Join Date: Aug 2006 Location: sfCA iTrader: (0)	Sorry I don't have your answer but this may help: Problem 1 force = mass x acceleration Since speed is constant, acceleration will be gravity. Since acceleration is gravity, the force is justified by the weight force = 65.2 kg (9.8 m/s2) at 10.4% more force: just find acceleration if force is increased by 10.4% acceleration = force(10.4%)/65.2
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05-31-2007, 03:07 AM	#9
BMWPower06 A^M=G is nothing w/o the Power of ///M 171 Rep 1,816 Posts Drives: ///M5 & ///M3 Join Date: Jan 2007 Location: Washington D.C. iTrader: (0)	Im out for the night, if any1 comes up with the answer please post __________________ Indianapolis Red BMW ///M5
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05-31-2007, 08:15 AM	#11
Josh49 Major General 252 Rep 6,664 Posts Drives: E90 325xi Join Date: Jan 2006 Location: Boston, MA iTrader: (33)	I'm at work and the pictures are not working for some reason... In any case, for the first one, are there pulleys involved? If so, you need to include the mechanical advantage that you gain by including pulleys in the system.. I think that is the link you are missing.. __________________ E90 325XI, MYSTIC BLUE ON BLACK/ALUM, STEP, NAV, PDC, CWP, XENON, SIRIUS, ALARM, MUD GUARDS, CLEARBRA, CHROME GRILLS AND TIPS, VALENTINE 1 (HARDWIRED), HO CERAMIC 40%, 161'S, REAR FOG MOD, LUX 4.0, BLACKLINES, OEM PEDALS, MTEC FOGS, GRUPPE-M REP INTAKE. 156'S AND RUBBER MATS FOR THE WINTER.
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05-31-2007, 10:35 AM	#12
hks786 Major General 2169 Rep 5,364 Posts Drives: * Join Date: Mar 2006 Location: UK iTrader: (0)	Basically she has to overcome her true weight which is 65.2kg x 9.8m/s^2 and also note that the speed is constant so there is NO acceleration in the first part of this question. Therefore answer is: F = ma = 65.2 x 9.8 = 638.96N downwards. (this is the force she needs to pull the rope at) By increasing the force by 10.4% we achieve a force of 705.41N downwards (by calculation). Then: a = F/m = 705.41/65.2 = 10.8 m/s^2 But you said this gave the wrong answer. Hmm, I’m not sure but I would think it is the right answer. She has to overcome her true weight (mass x gravitational force) to get a constant upwards speed. A constant upwards speed also means there is NO acceleration. Then you just have to calculate 10.4% of your answer from part 1 and then add it to the answer from part 1, this will give you the total force. Then just use a = F/m to calculate the acceleration. That is what I would do, but you said it’s wrong… __________________ Last edited by hks786; 05-31-2007 at 01:01 PM..
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