Download newtons 2nd law review

Newton’s Laws
Review Quiz
Newton’s Laws
• What is Newton’s second law (in words)
• Acceleration is proportional to force and
inversely proportional to mass
Newton’s Laws
• What is Newton’s Second Law,
mathematically?
• F=ma
Newton’s Laws
• What is Newton’s First law (in words)
• An object in motion (or at rest) stays in
motion (or at rest) unless acted upon by an
outside force
• Why cant you lift yourself off the ground by
puling up on your belt?
• A: because there is no outside force internal forces do not cause motion
Newton’s Laws
• What does proportional mean?
Newton’s Laws
• What are the two factors that determine
how much friction there is between two
objects?
• Normal force, coefficient of friction of the
materials
Newton’s Laws
• Does a larger block with the same mass
have more, less or the same friction
• same - surface area is not in the
calculations, does not matter
Newton’s Laws
• What is pressure?
• Amount of force per unit area
Newton’s Laws
• What are the units of pressure?MKS?
English?
• Pascals = 1newton/meter2
• Pounds/in2 = psi
Ramp Problem
• A 12 Kg block sits on a 40 degree ramp with a
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coefficient of sliding friction of .4
Find: Fwt
Fax
Fn
Ff
Fnet
a
*challenge - what µ so that it does not slide
Pressure
• A 140kg skater stands on one skate blade
that is 10 cm x 1 cm. What is the pressure
on the blade?
Newtons Laws
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Accelerations are produced by
a. forces.
b. velocities.
c. accelerations.
d. masses.
e. none of the above
Newton’s Laws
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The SI unit for force is equal to:
a) kilogram
b) kilogram-meter/s2
c) pound
d) slug
• and is called the ____________
Newton’s Laws
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If an object is at accelerating, we know that
a) Fnet = 0
b) It is falling
c) there is a net force on it
d) there is no friction
Newton’s Laws
• If the net force on an object is zero it must
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be:
a) at rest
b) have friction
c) accelerating
d) be at a constant velocity or at rest
• A 20 kg box is on a surface that has a
µ=.25 It is accelerating at 2m/s2.
• Draw a force diagram
• What is the applied force?
• How far will it go in 2 seconds?
• When a woman stands with two feet on a scale,
the scale reads 500 N. When she lifts one foot,
the scale reads
• a. less than 500 N.
• b. more than 500 N.
• c. 500 N.
• What is the difference between weight and
mass? Which stays the same on the moon vs
earth?
• When a woman stands with two feet on a scale,
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the scale reads 500 N. When she lifts one foot,
the pressure on her foot
a. Stays the same
b. Decreases
c. Doubles
D. Cannot be determined
• Suppose the force of friction on a sliding object
is 13 N. The force needed to maintain a
constant velocity is
• a. more than 13 N.
• b. 13 N
• c. less than 13N.
• A 1800g block is pulled by a 1200 gram
hanging mass. µ = .2 What is the
acceleration of the cart?
• What is terminal velocity? Draw a force
diagram of an object at terminal velocity.
• Why do a coin and a feather fall with the
same acceleration if there is no air?