Sponge - A 200 kg hockey player pushes a 150 kg official after receiving a penalty. If he pushes with a force of 500 N, what is the acceleration of each person?

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Sponge - A 200 kg hockey player pushes a 150 kg
official after receiving a penalty. If he pushes
with a force of 500 N, what is the acceleration
of each person?
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Newtons Law of Universal Gravitation - every
particle in the universe exerts a force on every
other particle by the following
equation F G m1m2 /r2G 6.67259 x
10-11 Nm2/kg2
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G is the universal gravitational constant. It
was first measured by Henry Cavendish
(1731-1810) over 100 years after Newton wrote
the law.
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The forces between two particles are an
action-reaction pair, as in Newtons third law.
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Ex. 5 - What is the magnitude of the
gravitational force that acts on each particle,
assuming m1 12 kg, m2 25 kg, and r 1.2 m?
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The value r must be measured from the centers
of the objects if they are not particles.
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The weight of an object is the gravitational
force that the Earth exerts on the object.
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If W is weight, Newtons law of gravitation
becomes W G MEm2 /r2
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Ex. 6 - The mass of the Hubble space telescope is
11 600 kg. Determine the weight of the telescope
(a) when it was resting on the Earth and (b) as
it is in its orbit 569 km above the Earths
surface.
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Relation Between Mass and Weight - W G
ME m2 /r2 W m gg is determined by G, ME,
and r.
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The normal force FN is one component of the force
that a surface exerts on an object with which it
is in contact, namely, the component that is
perpendicular to the surface.
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The forces on the block are balanced. Adding
another downward force causes FN to increase.
Adding an upward force, subtracts from W and FN
decreases possibly to zero.
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Ex. 8 - In a circus balancing act, a woman
performs a headstand on top of a mans head. The
woman weighs 490 N, and the mans head and neck
weigh 50 N. It is primarily the seventh cervical
vertebra in the spine that supports all the
weight above the shoulders. What is the normal
force that this vertebra exerts on the neck and
head of the man (a) before the act and (b) during
the act?
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When a person is accelerated upward or downward,
the apparent weight is greater or less than the
true weight. FN mg maa is if upward, -
if downward
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If a person is in free fall, a -g and by FN
mg ma, FN zero. The apparent weight in
free fall is zero.
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Friction is a parallel force to the direction of
intended motion.
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Friction before an object starts to move is
static friction. The maximum static frictional
force, fSMAX, is the maximum frictional force
that can be applied before motion and
acceleration occur.
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The ratio of fSMAX to FN is called the
coefficient of static friction. It is represented
by µS. fSMAX µS FN
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fSMAX µS FNThis equation relates only the
magnitudes of the vectors, not the directions.
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Ex. 8 - A sled is resting on a horizontal patch
of snow, and the coefficient of static friction
is µS 0.350. The sled and its rider have a
total mass of 38.0 kg. Determine the horizontal
force needed to start the sled barely moving.
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When two surfaces are moving across each other,
the friction is called kinetic friction fK. It is
usually less than static friction. µK is the
coefficient of kinetic friction. fK µK
FN
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Ex. 10 - A sled is traveling at 4.00 m/s along a
horizontal stretch of snow. The coefficient of
kinetic friction is mK 0.0500. How far does the
sled go before stopping?
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