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motion question

motion question - Physics Forum

motion question - Physics Forum. Discuss and ask physics questions, kinematics and other physics problems.


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Old 06-23-2003, 02:57 AM
Mike Purcell
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Default motion question



Interesting, everyone is correct with a few exceptions. In the
original problem knowing the force used to hit the puck is not enough.
You need to know either the distance or the time over which the force
was applied to determine the initial speed of the puck or you need to
know the initial speed. Tony had the most efficient solution if you
knew the energy applied by hitting the puck.
Maginsta's mistakes seem purposeful but may just signify an
ignorance of mathematics: "Sin Force = mass * acceleration, and
constancy would define acceleration as 0, how can a force exist?" I
would assume that "Sin" is a typo and should read "Since" but
mathematics is the language of physics and in mathematics "Sin" is a
trigonometric function. In "Absent acceleration, how do you derive a
force as being a constant?" no acceleration means no force and derive
is a calculus term meaning a rate of change and if the rate of change
is constant then it is changing constantly. However, impulses usually
involve a changing force in which case you need to know the rate at
which it is changing or the average force otherwise knowing the
distance or time in which it is changing will not give you the energy
imparted to the puck.
Mr. Watland's mistake involved "(i) Impulse = (Driving Force) *
(Time of Application of Force)". Looking at the units; impulse has
units of momentum or length squared divided by time squared while
force (mass multiplied by length divided by time squared) multiplied
by time has units of mass times length divided by time. They are not
equal.
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