By geometry, tan θ = 2000 m/5400 m. The pilot has to look down at an angle of 20°.Rapid Review
• Average speed is total distance divided by total time. Instantaneous speed is your speed at a particular
moment.
• Velocity is the vector equivalent of speed.
• Acceleration is a change in velocity divided by the time during which that change occurred.
• Displacement is the vector equivalent of distance.
• The three “star equations” are valid only when acceleration is constant.
• To solve any constant-acceleration kinematics problem, follow these four steps:
° Write out a table containing all five variables—v 0 , v (^) f , x − x 0 , a, t —and fill in whatever values
are known.
° Count variables. If you have three known values, you can solve the problem.
° Use the “star equation” that contains your known variables.
° Check for correct units.
• When an object falls (in the absence of air resistance), it experiences an acceleration of g , about 10
m/s^2 . It’s particularly important for problems that involve falling objects to define a positive direction
before solving the problem.
• An object’s motion in one dimension does not affect its motion in any other dimension.
• Projectile motion problems are usually easier to solve if you break the object’s motion into
“horizontal” and “vertical” vector components.
• The slope of a distance–time graph is velocity.
• The slope of a velocity–time graph is acceleration.
• The area under a velocity–time graph is displacement.