PS112: Physics

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PS112 Physics

• By Somchai Thangsathityangkul Lecture 4 One
  dimension motion (Continue)

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Constant velocity motion

• An object move with an uniform motion
• slope of x(t)
  constant

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Acceleration
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EXAMPLE
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Constant Acceleration

• For constant a(t) a
• if object is at
  x0 at time t0
• after an elapsed
  tim t it
• will be at

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Constant Acceleration

• Since v(t) increases uniformly with t

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Constant Acceleration

• We have
• So,
• Then ,

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Constant Acceleration

• Using calculus

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Example

• How long does it take a car to travel 30 m if it
  accelerates from rest at a rate of 2.0 m/s2 ?
• Solution Known x0 0, v0 0 , a 2.0 m/s2,
  x30 m ? t ?
• from eq

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Example

• Particle is at the coordinate position x05m at
  t0 and moving with a velocity v020 m/s. The
  particle then starts to decelerate. At t10 s the
  particle has a velocity v2 m/s
• a) What is the acceleration ?
• b) What is the position function ?
• c) How long is it before the particle returns
  to x5m.

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EXAMPLE

• A car traveling at a constant speed of 45.0 m/s
  passes a trooper hidden behind a billboard. One
  second after the speeding car passes the
  billboard, the trooper sets out from the
  billboard to catch it, accelerating at a constant
  rate of 3.00 m/s2. How long does it take her to
  overtake the car?

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Try this

• An alpha particle travels along the inside of a
  straight hollow tube 2.0 m long which forms part
  of a particle accelerator.
• a) If one assumes uniform acceleration, what
  is the acceleration of the particle, if it enters
  at a speed of 1.0x104 m/s and leaves at 5.0x106
  m/s ?
• b) How long is it in the tube ?

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Try this

• You break your car from a velocity of 85 km/hr to
  45 km/hr over a distance of 105 m.
• a) What is the acceleration ?
• b) How much time elapses during this interval
  ?
• c) If you were to continue braking with the
  same acceleration, how much longer would it take
  for you to stop and how much additional distance
  would you cover ?