Chapter 5 Newtons 2nd Law Law of Accel

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Chapter 5Newtons 2nd Law- Law of Accel

• Problems 1-11
• Indicates problems are honors level challenge
  problems
• All are welcome to try them!!
• 6, 9d, 10h

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Practice Problems Page 1

• F mass x accel
• F m x a
• F 40kg x 4m/s2
• F 160 N
• Mass Force/accel
• m F / a
• m 100N / 1m/s2
• m 100kg
• Accel Force/mass
• a F/ m
• a 12 N / 2kg
• a 6 m/s2
• Force mass x accel
• Fnet m x a
• Fnet 2kg / 10 m/s2
• Fnet 20 N

• a) since the elevators weight is 10,000N then the
  tension force is 10,000N upward in the cable
• b) a Fnet/ mass
• 2m/s2 (Fsupport Fgravity) / 1000kg
• 2m/s2 (Fsupport 10,000N) / 1000kg
• 2000 kg m/s2 Fsupport 10,000N
• Fsupport 12, 000N

If the net force is larger in the upward
direction then the accel will be upward.
10, 000N
c) a Fnet/ mass 3 m/s2
(Fgravity Fsupport) / 1000kg 3 m/s2
(10,000 N Fsupport) / 1000kg 3000 kg
m/s2 10, 000 N Fsupport Fsupport 7,000
n
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Practice Problems Page 1

• a) b)

• a) b)

4
F-18 on an aircraft carrier takeoff videos

• Rear View ? Looking back
• http//www.boeing.com/defense-space/military/fa18/
  video/f18lkbk.mov
• Underside view of airplane
• http//www.boeing.com/defense-space/military/fa18/
  video/chnmnt.mov
• Side view of airplane
• http//www.boeing.com/defense-space/military/fa18/
  video/f18catlch.mov
• (control click on a link to launch directly from
  powerpoint)
• Requires Quicktime (most of you have it if you
  have iTunes on your computer)

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Practice Problems Page 2

• a) if I pull the box with 80N of force while
  there is 100N of friction the pull will not be
  able to overcome the static friction ? remain at
  rest
• b) 100N pull and 100N friction Fnet of 0N,
  therefore the acceleration is 0m/s2 ?
  Equilibrium
• c) 200N pull and 100N friction Fnet of 100N in
  direction of pull

d) 620N pull and 100N of friction Fnet of 520N
in direction of pull
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Practice Problems Page 2

• a) if I pull the box with 80N of force while
  there is 100N of friction the pull will not be
  able to overcome the static friction ? remain at
  rest
• b) 100N pull and 100N friction Fnet of 0N,
  therefore the acceleration is 0m/s2 ?
  Equilibrium
• c) 200N pull and 100N friction Fnet of 100N in
  direction of pull

d) 620N pull and 100N of friction Fnet of 520N
in direction of pull
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Practice Problems Page 2

• a)
• b) a 10m/s2 because there is no air resistance
• c) as the velocity increases, so does the air
  resistance (put your arm outside the window of a
  car moving 10mi/hr versus 60mi/hr!!)
• d) yes, still speeding up because Fg is greater
  than air resistance so net force is down as is
  the acceleration
• e) when air resistance equals weight the
  skydiver is at terminal velocity
• f) when at terminal velocity and forces are
  equal and opposite (Equilibrium) accel is 0m/s2
• g) air resistance is much larger than weight so
  net force is 3750N 750 N or 3000N upward
• h) acceleration is a negative value (slowing
  down) when the parachute is open

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Practice Problems Page 2

• a) 40 kg 400N (mass x gravity weight)
• b) when walking on 2 feet your weight is split ½
  on each leg
• c)

d) Yes, the first step you put on the pond and
the pressure will break the ice. e) Since
surface area is inversely proportional to
pressure, increasing area will decrease pressure
LAY DOWN!