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Review TAKS Physics

Review TAKS Physics. Motion Motion can be described as change in position of a body. Average velocity (speed) is the change of distance of an object over time . Velocity Graphs V = distance time

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Review TAKS Physics

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  1. Review TAKS Physics

  2. Motion Motion can be described as change in position of a body. Average velocity (speed) is the change of distance of an object over time . Velocity Graphs V = distance time Velocity (v) is the slope (rise over run) of a distance (d) vs. time (t) graph.

  3. 1. Given: speed= 1600m/s Time = 1.5 x 10-5 s Distance = speed x time 1600m/s x 1.5x 10 -5 s =.024 m = 24 mm = D

  4. 2. Joe Cool, Lee track star, ran 600 meters at 10m/sec. How long did it take Joe to run the race? Distance= 600m Speed = 10 m/s Time = distance/speed 600m / 10 m/s = 60s

  5. Q= 14Km/12 min=1.17km/min R= 12km/8min= 1.5 km/min S = 15km/9 min =1.67 km/min- This is the greatest speed

  6. Distance moved= 3cm time = 2second Speed = 3cm/2 second =1.5 cm/s Answer - A

  7. When an object’s speed changes over time it is accelerating (or decelerating) A = V final – V initial time Units for acceleration or m/s2 Acceleration Acceleration (a) is the SLOPE of a VELOCITY (v) vs. time (t) graph Plotted on a distance vs. time graph, acceleration is an exponential curve The slope of a velocity –time graph represents ACCELERATION Acceleration is a change in an objects velocity (speed or direction)

  8. A fighter jet landing on aircraft carrier’s flight deck must reduce its speed from about 153 m/s to exactly 0 m/s in 2 s. What is the jet’s acceleration? A = Vfinal – Vinitial time 0 m/s – 153 m/s = -76.5 m/s2 2 s

  9. A = Vfinal – Vinitial time 6.5m/s-6.5m/s = 0 m/s2 4 s

  10. Definition of a Force • A Force is a push or a pull The unit of force is Newton.

  11. Balanced Force • A force that produces no change in an object’s motion because it is balanced by an equal, opposite force.

  12. Are forces that results in an object’s motion being changed. Unbalanced Forces + =

  13. Friction A force that acts in a direction opposite to the motion of two surfaces in contact with each other.

  14. Friction Friction causes an object to slow down and stop. Since the amount of energy stays constant, the energy becomes heat.

  15. Answer –A . More force exerted less time it will take .

  16. Answer: D. An opposing force acted on the puck.

  17. Newton’s 1st Law-

  18. Inertia or Newtons 1st Law • Tendency for an object to stay at rest or moving in a straight line at a constant speed. • The mass (symbol is “m”, measured in kg) of an object determines its inertia

  19. Newton’s Second LawAcceleration is produced when a force acts on a mass. The greater the mass (of the object being accelerated) the greater the amount of force needed (to accelerate the object). F = ma So, if the mass (m) is 1000 kg and the acceleration (a) is .05 m/s2 then: F = 1000 kg x .05 m/s2 = 50 N

  20. Weight (pull of gravity) is a commonly measured force (measured in N), calculated by F=mg, g is the acceleration due to gravity 9.8 m/s2

  21. 1. If the weight of an object is 60 N on earth what is its mass? Weight = mg Mass = weight / acceleration due to gravity 60 N / 9.8 m/s2 6.12 kg

  22. Force = m x a a = 44.7 m/s- 0 m/s = 9.93 m/s2 4.5 s m = 90.0 kg F = 90.0 kg x 9.93 m/s2 = 894 N

  23. B. For every action there is an equal and opposite reaction. s2

  24. D. Since the ball will go forward ,so the student will go backward.

  25. Force = m x a = 1300 kg X 1.5m/s2 =1950 N

  26. Force = mass x acceleration Mass of smaller skater = 40 kg Acceleration of smaller skater = 3.0 m/s – 0 m/s = 2.5 m/s2 1.2 s 40 kg x 2.5 m/s2 = 100N

  27. D. The scallop will move in the opposite direction.

  28. 15. What is the weight of a rock that has a mass of 5.0 kg? 0.51 N 49 N 0.51 Kn 49 kN Weight = mg = 5.0 kg x 9.8 m/s2 = 49 N Answer: B

  29. 16. Airbags on cars are used to keep you from hitting the steering wheel of the car when the car hits a stationary object, because your body still has – resistance force potential inertia D. INERTIA

  30. Why use a machine? • In an ideal (perfect) machine the work put into the machine equals the work put out by that machine (Win = Wout) • Why is this impossible?

  31. No real machine is 100% efficient… They do not put out the same amount of work that is put in. Efficiency of a machine is work output / work input x 100 % Efficiency = Wout x 100% Win

  32. Machines make work easier • The ideal mechanical advantage (IMA) of a machine is the number of times the output force is larger than the input force IMA=Fout/Fin • A machine can only make this happen by moving the input force through a farther distance than the output force • Fin • din = Fout • dout

  33. Total work out put = 6N X 3m = 18 J Work input = 30 J Work converted to heat = 30 J -18J = 12 J

  34. 18a. An Automobile engine produces 15J of work for every 100J of energy consumed. What is the engine’s efficiency? % Efficiency = work input x 100% work out put = 15 J x 100% 100 J = 15 %

  35. 18b. If a machine is 36% efficient and can provide 75J of work output, how much work must be put in the machine? Efficiency = Wout x 100% Win 36% = 75 J X 100% Win Work input = 75 J X 100% 36% = 208 J

  36. Simple machines make our work easier by enabling us to use less mechanical effort to move an object. Often several simple machines are combined in complex machines. Remember, the ideal mechanical advantage of a machine (IMA) is the number of times the output force is larger than the input force IMA = Fout/Fin A machine can only make this happen by moving the input force through a further distance than the output force

  37. We use machines to reduce the amount of force applied, but at the sake of more TOTAL work required.

  38. 6 Types of simple machines • Some Simple Machines: • Inclined planes • Screws • Pulleys • Wheel and axle • Levers • Wedge

  39. Work • Work: using a force for a distance • W = F x d • The work done by forces on an object = changes in energy for that object. • Work and Energy are measured in Joules • 1 Joule = 1 Newton • meter

  40. When you push a wall and the wall does not move, the distance moved is zero, so the work done is zero too.

  41. W= F X D = 980N x 2.04 m = 2000J

  42. Work = F X D 200 N x 5 m = 1000 J Answer: B

  43. Energy Is defined as the Ability to do Work Energy has Two Types: • Kinetic (Energy of Motion) and • Potential (Stored Energy)

  44. Kinetic Energy KE = ½ m v 2 Ex: A moving car has the ability to do work on the light pole if it hits it.

  45. K.E. = ½ mv2 50 J= ½ (1 kg) v2 100= V2 V= 10 m/s

  46. Circle the one that has more kinetic energy A 25 kg mass or a 30 kg mass going 5 m/s. Two 10 kg masses, one going 75 m/s, one going 45 m/s. A car at rest or a car rolling down a hill. A heavy bike or a light bike.

  47. Potential Energy2 possibilities Potential energy (PE) is stored energy 1. Gravitational PE Ex: Object lifted to some height 2. Elastic PE Ex: A stretched or compressed object (spring or rubber band )

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