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Q: Basic Mechanical Physics ( No Answer,   7 Comments )
Subject: Basic Mechanical Physics
Category: Science > Physics
Asked by: cchanceus-ga
List Price: $5.00
Posted: 19 Sep 2006 17:25 PDT
Expires: 19 Oct 2006 17:25 PDT
Question ID: 766776
I am disputing these questions with a fellow peer and would like a
professional to finalize this debate.

1. A person walking on a level surface moves forward because the forces of?
a) his feet pushing on the ground
b) the ground pushing on his feet
c) either

2. Newton's second law states that if a net force acts on an object,
it will move at constant velocity
a) True
b) False
There is no answer at this time.

Subject: Re: Basic Mechanical Physics
From: qed100-ga on 19 Sep 2006 22:37 PDT
Here's a summary of Newton's three laws of mechanics. It should help
you to clarify the problems.

[1]- Inertia. A body's motion is quantified by its momentum (p), which
is proportional to both its mass (m), and its velocity (v). In other
words, p = mv. Changing velocity = acceleration (a).

    A body of constant mass in isolation travels with zero
acceleration: it neither speeds up nor slows down, nor does it change
direction. In other words, its momentum doesn't spontaneously change
by itself. It has inertia.

[2]- Force. Changing momentum = force, F. Force is quantified as F = ma.

[3]- Conservation of momentum. Forces are induced via interactions
between pairs of bodies, A & B. An interaction between A & B will
leave their total momentum unchanged. In other words, if A alters B's
momentum by amount d, then B changes A's momentum by -d. The two
amounts add up to zero overall. A & B exert equal sized forces upon
each other, but in opposite directions. Whether A & B are attracting
or repelling, there will be a unique point between them, their
mass-center, which has its own momentum, which is the total momentum
of the two bodies A & B.
Subject: Re: Basic Mechanical Physics
From: cchanceus-ga on 20 Sep 2006 18:00 PDT
I believe the answer to the first question is either and the second
question is true. I am being told my answers are incorrect. Thoughts?
Subject: Re: Basic Mechanical Physics
From: barneca-ga on 20 Sep 2006 20:11 PDT
i wouldn't normally answer what i suspect is an obvious homework
question, but i think question 1 is somewhat poorly worded, at least
for a beginner.  an object accelerates because of forces applied to
that object, not because of forces that object applies to other
things.  your thought that it is "either" shows you know the two
forces have equal magnitude, but you have to also understand that they
are in opposite directions.  which force is in the same direction as
the person's motion?

qed100 has answered question 2 for you, all you have to do is read
(and understand) what they wrote.

if you plan on spending $5 for every homework problem you get stuck
on, your parents are NOT going to be happy (or, if you're older and
paying your own way, you could have bought a pitcher at happy hour
with that).  whether you're in high school or college, teachers,
professors and teaching assistants have already been paid, by you, to
help you with this stuff, all you need to do is go to their office
hours and ask for help.

Subject: Re: Basic Mechanical Physics
From: ashokrr-ga on 22 Sep 2006 09:11 PDT
my naswer to this is that if u are walking on the surface u act some
force on whaich has vbeen the positive force where according to netons
laws of equal  and oppsite and equal reaction he same amount of force
is exerted on the  foot u hav exerted on the surface here u can bee
made to walk furhter which helps u in the direction of the force. if u
sudddnely move oppsirte the force of replusion acting on the foot with
the accleraion of the body reples u to undisurb and u may fall these
are things two got unnoticed in the walk.
if a net force acts on the body its to move if u are thing that if the
force is acting on the stone its not moving u can see them as a hill
is not moving though some force id=s acting on the every body exised
in the universe
Subject: Re: Basic Mechanical Physics
From: harrysnet-ga on 06 Oct 2006 15:51 PDT
1. Answer is (b) the ground pushing on his feet.

When you are stationary and start moving is because a force is acting on you.
Of course this is generated by the action-reaction law when your feet push 
the ground, but that is not moving you (in theory it moves the whole earth
backwards and very tiny amount backwards).

2. Answer is (b) False.

A force causes acceleration, that is a velocity change. So a non zero force 
will cause continuous acceleration (it doesn't even have to be constant), 
which means that the velocity changes continuously.
Subject: Re: Basic Mechanical Physics
From: ukbikerman-ga on 13 Oct 2006 03:48 PDT
Surely the answer is neither. Force needed is horizontal and the only
choices are vertical. Without the coefficient of friction then guy is
going nowhere,,,
Subject: Re: Basic Mechanical Physics
From: barneca-ga on 13 Oct 2006 06:58 PDT
"...the only choices are vertical..."

it doesn't say that anywhere in the question.


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