Ask Experts Questions for FREE Help !
Ask
    dragosani's Avatar
    dragosani Posts: 6, Reputation: 1
    New Member
    		  
    #1

    Feb 18, 2009, 01:57 PM
    acceleration just a check.
    A 12.0 kg bucket is lowered vertically by a rope in which there is 163N of tension at a given instant. What is the acceleration of the bucket? Is it up or down?
    This is what I've done.

    f=ma
    163N=12.0kg a
    163N/ 12.0kg = a
    13.6 m/s^2 = a

    That should put the bucket going up since it's positive . But it starts saying it's being lowered and I don't really know how the force of gravity fits into it. Any help is appreciated. Thank you
    ebaines's Avatar
    ebaines Posts: 12,131, Reputation: 1307
    Expert
    		  
    #2

    Feb 19, 2009, 09:32 AM

    It helps to draw a free-body diagram for problems like this. Your diagram would show the bucket with an upward force of 163 N, and a downward force due to its weight. The resultant force that you have from combining these two forces components is what determines the acceleration of the bucket, using F=ma. If you find a is a positive number, that means the bucket is accelerating upward, but it does not necessarily mean that the velocity is in the up direction - perhaps the bucket is being lowered at a decreasing downard velocity (ie. slowing its rate of descent).
    Wuerschti's Avatar
    Wuerschti Posts: 30, Reputation: 1
    Junior Member
    		  
    #3

    Mar 18, 2009, 10:22 AM

    Think about this gravity on earth is 9.8m/s^2

    The ONLY way this bucket can accelerate towards the ground faster than 9.8m/s^2 is if it had a net force pushing it down. Since there is tension in the rope we know the net force is in the opposite direction of gravity. THEREFORE, before even attempting this problem, we know the answer must be a fraction of 9.8m/s^2

    f=tension-ma
    f=163-(12kg)(9.8m/s^2)
    f=163-117.6
    f=45.6

    f=ma
    45.6=12(a)
    a=45.6/12
    a=3.8m/s^2 downwards
    Wuerschti's Avatar
    Wuerschti Posts: 30, Reputation: 1
    Junior Member
    		  
    #4

    Mar 18, 2009, 10:23 AM
    Sorry, "Since there is tension in the rope we know the net force is in the opposite direction of gravity"
    I meant the force of tension is upwards and the force of gravity downwards. The net force is downwards
    ebaines's Avatar
    ebaines Posts: 12,131, Reputation: 1307
    Expert
    		  
    #5

    Mar 18, 2009, 10:32 AM
    Quote Originally Posted by Wuerschti View Post
    Sry, "Since there is tension in the rope we know the net force is in the opposite direction of gravity"
    I meant the force of tension is upwards and the force of gravity downwards. The net force is downwards
    Sorry - the net force is upwards. The tension in the rope upwards is greater than the weight of the bucket; hence the net force is upwards (as your own math shows). Thus the acceleration is upwards.
    Wuerschti's Avatar
    Wuerschti Posts: 30, Reputation: 1
    Junior Member
    		  
    #6

    Mar 18, 2009, 04:02 PM

    Yea that's what I meant, I just confused myself twice.
Not your question? Ask your question View similar questions
 

Question Tools Search this Question
Search this Question:

Advanced Search

Add your answer here.


Check out some similar questions!

My ife is receiving a disability check, and I think a Social Security check [ 2 Answers ]

My wife is receiving a disability check, and a Social Security check, can I claim part of it?If he is out of the country and I have proven parternity will he be arrested so I can claim everything?

Where do you find the plug in to check the check engine light [ 16 Answers ]

I am trying to find the plug in where you plug in the computer to check the check engine light it a 1992 civic can anyone tell me where it located at and if you have picture that would be great thanks if you could tell me the color of the plug in and how many pin in it that would help me in finding...

Disability check VS. Child support check [ 2 Answers ]

My sister lives w/ my step father. My mom HAD to leave the home. My sister is 13 and decided to stay w/ father. I don't think he can take care of my sister.. he can't hardly take care of his self. He receives a disability check for his self and my sister gets one also until she is 18. He BLOWS...

Substituting derivative of acceleration for acceleration [ 1 Answers ]

Can the derivative of acceleration be subsituted for a in f=ma?

Acceleration [ 1 Answers ]

A dare devil is shot out of a cannon at 45 degress to the horizontal with an initial speed of 25 m/s. A net is positioned a horizontal distance of 50 m from the cannon. A. At which height above the cannon should the net be placed in order to catch the daredevil? B. At which velocity does the...

View more questions Search