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## Chapter 5 Projectile motion

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**1. Recall: a projectile is an object only acted upon by**gravity**2.Chapter 4: [linear motion]straight line motionthat was**ONLY vertical or ONLY horizontal motion**3. Chapter 5: looks at motion that followsa diagonal path**or a curved path**5. We will separate curved motion into independent x and y**motions**6. vertical motion is not affected by the horizontal**motion. And the horizontal motion is not affected by the vertical motion.**7. Observe: a large ball bearing is dropped at the same**time as a second ball bearing is fired horizontally.**Remember adding 2 perpendicular vectorshorizontal and**vertical vectors.**8. Remember: When we add perpendicular vectors we use**Pythagorean theorem to find the resultant.**12. Suppose the motor moves the boat at 15 m/sec.how fast**will the boat travel downstream [with the current]?**Total velocity traveling downstream: Vtotal= Vboat +**Vcurrent= 15 + 8 = 23 m/sec **14.Using motor against the current: total velocity**traveling upstream [AGAINST the current] Vtotal = Vboat –Vcurrent**15. Going upstream: Velocity of current and boat are**opposite directionsVtotal = Vboat –Vcurrent**16. If there was no current, how many seconds for the boat**to travel 120 meters to reach the opposite side?**time = distance velocitytime = 120 m**15 m/sectime = 8 seconds**But there if is a current, what happens when you try to**go straight across the river from A to B?**18. If there is a current, The boat still crosses in 8**seconds, but it lands downstream at point C**19. Add the perpendicular velocity vectors add to find the**resultant velocity**20. In this example, Every second the boat travels 15 meter**in the x direction IT ALSO TRAVELS 8 meter in the y direction**How far down stream is the boat when it reaches the opposite**shore?**Velocity = distance timeso distance = velocity X**timedistance = 8 m/sec X 8 sec = 64 m**What if you want to travel straight across and land at B,**not C?**21) If you want to go from A to B instead, you must point**the boat diagonally upstream to compensate for the current.**25. crosswind: blows plane off course [wind perpendicular**to direction of plane]**Vx2 + Vy2 = Vboat2Vx2 + 82 = 152Vx2 =225-64 = 161Vx =12.7**m/sec**How many seconds to cross?**From A to BT = D/VT = 120/12.7 T = 9.4 sec