KINS 382 LAB 15

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KINS 382 - LAB 15

• Energy Problems

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Formulae

• PE KE, when gravity is the only external force
• PE (m)(a)g(h)
• PE wt(ht)
• KE 1/2 mv²
• Work F x d
• Power F x d/t or F x V

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Question 1

• What is the kinetic energy of a 10kg medicine
  ball traveling at 3 m/s.

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Answer 1

• m 10kg, V 3 m/s, KE ?
• KE 1/2mV²
• KE 1/2(10kg)(3m/s)²
• KE 5kg (9m²/s²)
• KE 45 kg(m²/s²)
• KE 45 Joules (or J)

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Question 2

• How fast is a 10 pound ball moving if it has 50
  Joules of kinetic energy?

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Answer 2

• wt 10lb, KE Nm, V ?
• KE 1/2mV², or V² KE/.5(mass)
• Convert 10lbs to 4.54 kg
• V² 50Nm / .5(4.54kg)
• V² 50 kg(m²/s²) / 2.27kg
• V² 22.03 (m²/s²)
• V
• V 4.69 m/s

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Question 3

• Determine the mass of an object traveling at 12
  m/s with a kinetic energy of 200 Joules.

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Answer 3

• V 12m/s, KE 200 Nm, m ?
• KE 1/2mV², or m 2KE/V²
• m 2(200Nm) / (12m/s)²
• m 400Nm / 144m²/s²
• m 2.78kg

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Question 4

• In the two following situations, which will
  generate more energy?
• A 150lb man who jumps from a height of 20 m, or a
  .50 lb ball traveling at 100 mi/hr?

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Answer 4

• wt1 150lb, ht1 20m
• PE ht(wt), 150lb x 4.45N/1lb 667.5N
• PE 20m(667.5N)
• PE 13,350 J

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Answer 4 (Cont)

• wt2 .50lbs, V 100 mi/hr
• 50lb x 1kg/2.2lb .23kg
• 100 mi/hr x .447m/s / 1mi/hr 44.7m/s
• KE 1/2mV²
• KE 1/2(.23kg) (44.7m/s)²
• KE .12kg(1998.09m²/s²)
• KE 239.77 Joules
• Scenario 1 will generate more energy!

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Question 5

• A balloon weighing 3 kg is dropped on Dr. Stulls
  head from a distance of 10 m.
• What is the balloons potential energy?
• Prove the KE of the balloon at impact is the same
  as the potential energy at release.

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Answer 5

• m 3kg, d 10m, PE ?
• 3kg x 9.81N / 1kg 29.43N
• PE wt(ht)
• PE 29.43N(10m)
• PE 294.3 Joules

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Answer 5 (Cont)

• Prove KE PE
• Find time using Free fall equations, t 1.43s
• Vf Vo a(t)
• Vf 0 9.8 m/s²(1.43s)
• Vf 14.01 m/s
• KE 1/2mV²
• KE 1/2(3kg) (14.01m/s)²
• KE 1.5kg (196.28m²/s²)
• KE 294.42 Joules

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Question 6

• Megan (110 lbs.) jumps off a 5 m log into the Eel
  river.
• What is the work done on her by gravity?

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Answer 6

• wt 110 lb, d 5m, w ?
• 110 lb X 4.45N / 1lb 489.5 N
• W F x d
• W 489.5N (5m)
• W 2447.5 Joules or Nm

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Question 7

• If someones 8 pound earring falls into her plate
  of pasta with 42 J of kinetic energy, how fast is
  the earring moving when it hits the pasta?

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Answer 7

• wt 8lb, KE 42Nm or Joules, V ?
• 8lb x 1kg/2.2lb 3.64kg
• KE 1/2mV²
• 42Nm 1/2 (3.64kg) V²
• 42Nm 1.82kg V²
• 42Nm / 1.82kg V²
• 23.08 m²/s² V²
• V
• V 4.8m/s

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Question 8

• Sarah is late for biomechanics. She generates
  .75 hp from the Science A building to Forbes
  complex.
• How much power did she generate, measured in
  Watts?

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Answer 8

• hp .75, Power ?, 1 Watt 746 hp
• .75 x 1 Watt/746hp 559.5 Watt Power

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Question 9

• Jeremy throws a 10kg anatomy book at an
  unidentified instructor.
• If the velocity is 8.9m/s, how much kinetic
  energy does the anatomy book generate?

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Answer 9

• m 10kg, V 8.9m/s, KE ?
• KE 1/2mV²
• KE 1/2(10kg) (8.9m/s)²
• KE 5kg (79.21m²/s²)
• KE 396.05 Joules

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Question 10

• On a planet far, far away (with no physics
  classes required), the gravitational acceleration
  is 43 m/s².
• If my your weight on Earth is 145 pounds, how
  much would you weigh on this planet?

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Answer 10

• a 43 m/s², wt 145lb (Earth),
  wt ? (planet)
• 145lb x 1kg/2.2lb 65.91kg
• F ma
• F 65.91kg (43m/s²)
• F 2834.13 N
• F 2834.13 N x 1lb/4.45N 636.88lb

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Question 11

• A swimmer being chased by a shark acquires a
  constant speed of 2.83 m/s.
• Unfortunately, the drag force opposing the
  swimmers motion is 210N.
• What is the power of the drag force?

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Answer 11

• V 2.83m/s, F 210N, Power (Watts) ? (drag
  force)
• P W/t or P F x d/t or P F x V
• P 210N (2.83m/s)
• P 594.3 Watts

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Question 12

• Kari must pedal (45 rev/min) a stationary bike
  for 22 min a day for her recreation program.
• Her bicycle wheel (r .5m) has a frictional
  force of 22 lbs.
• Calculate the amount of work performed and the
  power she generates.

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Answer 12

• Bicycle Pedal speed 45 rev/min, t 22min r
  .5m, F 22lb, Work ?, Power ?
• Time 22min x 60s/1min 1320s
• Force 22lb x 4.45N 97.9N
• Radius .5m/rad(6.28rads) 3.14m
• d r(pedal speed)t
• d 3.14m(45 rev/min) 22min
• d 141.3 m/min (22min)
• d 3108.60m, we need distance to find work

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Answer 12 (Cont)

• W F x d
• W 97.9N (3108.60m)
• W 304,331.94 Nm or Joules
• Power Work/t
• Power 304,331.94 J / 1320 s
• Power 230.55 Watts

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Question 13

• Kim (120 lb) jogs on the treadmill (at a 4
  grade) for 22 minutes at 5 mi/hr.
• Calculate the amount of work she performs and the
  power she generates during her jog.

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Answer 13

• wt 120lb, ? 4, t 22min, V 5mi/hr, Work
  ?, Power ?
• 5mi/hr X .447m/s / 1mi/hr 2.24m/s
• 22min X 60s / 1min 1320s
• 120lb X 4.45N / 1lb 534N

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Answer 13 (Cont)

• ht sin(?)V(t)
• ht sin(4)(2.24m/s)(1320s)
• ht (.07)(2.24m/s)(1320s)
• ht .16m/s(1320s)
• ht 211.20m
• Work F(or weight) X d(or height)
• Work 534N(211.2m)
• Work 112,780.80 Joules

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Answer 13 (Cont)

• Power Work/t
• Power 112,780.80 Joules / 1320s
• Power 85.44 Watts

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Conclusion