Relative motion

1
Relative motion

• A Reference Frame is the place you measure from.
• Relative motion problem has
• 1) Stationary Reference Frame the one which
  does not move (observer on the ground)
• 2) Moving Reference Frame the one which moves
  (e.g. train)
• 3) Object of interest who moves relative to both
  reference frames
• Velocity of the object relative to the ground
  (to the Stationary Reference Frame) Velocity of
  the object relative to the Moving Reference Frame
  Velocity of the moving frame relative to the
  ground (to the Stationary Reference Frame)

2
Problem solving (relative motion)

• Problem 45 p. 75. IP The pilot of an airplane
  wishes to fly due north, but there is a 75 km/h
  wind blowing toward the east.
• (a) In what direction should the pilot head the
  plane if its speed relative to the air is 310
  km/h?
• (b) Draw a vector diagram that illustrates your
  result in part (a).
• (c) If the pilot decreases the air speed of the
  plane, should the angle found in part (a) be
  increased or decreased?

3
In class test
4
Problem solving (relative motion)

• Problem 47 p. 75. You are riding on a jet ski
  at an angle of 35 upstream on a river flowing
  with a speed of 2.8 m/s. If your velocity
  relative to the ground is 9.5 m/s at an angle of
  20.0 upstream, what is the speed of the jet ski
  relative to the water?

5
Problem from 2003 midterm (relative motion)

• A boat can travel at a speed of 20.0 km/h
  relative to water. The boat sails across a river
  (perpendicular to the river bank) and reaches a
  point 5.00 km directly across from its launch
  point. The water is flowing at a speed of 8.00
  km/h parallel to the river bank.
• At what angle must the boat have steered to reach
  its destination?
• How much time it required to make the trip?

6
Problem from last year midterm (Vectors)

• Vectors and are written as
• (a) Draw the vectors
• (b) Write the vector in unit notation
• (c) Write the vector in unit notation
• (d) Calculate the magnitude of the vector
• (e) Calculate the direction of the vector