PHY 101 1nd Edition Lecture 8 Outline of Last Lecture I 3 2 Components of a Vector II Vector Addiction Algebraically III 3 3 Displacement Velocity Acceleration in 2 Dimensions a Average Velocity b Instantaneous Velocity c Average Acceleration d Instantaneous Acceleration Outline of Current Lecture IV Projectile Motion V Velocity Components VI Displacement VII Direction of Velocity Current Lecture Projectile Motion Two dimensional free fall motion Motion can be decomposed in the x and y directions horizontal and vertical they are independent of each other o Initial velocity vi vox voy o Along x direction constant speed motion vx vox o Along y direction constant acceleration vy voy ayt A simple way of understanding decomposition of a 2D motion o Imagine that you shine a parallel light beam on a projectile Velocity Components o Decomposition of the velocity into x and y directions Initial velocity vox vcos voy vsin o Velocity at any time t vx vcos vy vsin o We also know that Vx vox constant Vy voy ayt voy gt These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute G 9 8m s2 Displacement o Motion in each direction is reduced to a one D motion o Along the x direction since ax 0 it is a constant velocity motion x voxt 1 2 ayt2 voyt 1 2 gt2 o This explains the parabolic path Direction of velocity o The magnitude of the velocity Pythagorean theorem o Initial vo vox2 voy2 1 2 o At time t v x2 y2 1 2 Direction of the initial velocity o tan 1 voy vox Direction of the velocity at time t o tan 1 vy vx Ex o A rescue plane is at a constant v 40m s horizontally at height of 100m above the ground the plane drops a package to a hiker o a where does the package land on the ground with respect to the position it was released from Draw coordinates when it hits the ground y displacement y 100m xdisplacement x voxt Use equations for free fall objects to find t y voyt 9yt2 9 8 m s2 t2 100 4 9t2 T2 100 4 9 t 4 5s o Therefore x voxt 40 4 5 180m Tip Use y to find time then use time to find displacement o B What are the horizontal and vertical components of the package s velocity right before it hits the ground Solution Horizontal Vx vox 40 m s Vertical Vy voy at ay g Vy gt t 4 5s Vy 9 8 4 5 Vy 44 m s o C What is the packages speed just before it reaches the ground Vx vpx 40m s vy 44 m s V vx2 vy2 1 2 V 402 44 2 1 2 59 5 m s o D what is the impact angle tan 1 vy vx 47 7
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