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# Wednesday – November 7

Wednesday – November 7. Review Exam on Friday. REVIEW. You are allowed on flash card. I will NOT provide formulas. What is the resultant of a pair of forces 100N upward and 75N downwards? 25N up. Why is speed scalar and velocity vector? Speed is only a number.

## Wednesday – November 7

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1. Wednesday – November 7 • Review • Exam on Friday

2. REVIEW • You are allowed on flash card. • I will NOT provide formulas.

3. What is the resultant of a pair of forces 100N upward and 75N downwards? 25N up

4. Why is speed scalar and velocity vector? Speed is only a number. Velocity is speed in a given direction.

5. What is the end point for: 45° for 3 blocks, S for 7

6. Calculate the resultant for the following: 8m east, 2m north, 6 m west 22+22 = √8 = 2.9m NE

7. A ball is dropped from a 60m high building. How far will it have fallen after 3.0 seconds? y = ½ gt2 4.8m/s2 x 9s2 = 44.1m

8. In the absence of air resistance, why does the horizontal component of velocity for a projectile remain constant? No other forces are involved.

9. A bird flies at 20km/h. How long does it take to fly 400km? 400km/ 20km/hr = 20hours

10. A rock is thrown at a target 40m away. It hits the target in 4.0 seconds. What is the speed of the rock? 40m/4.0 seconds = 10m/s

11. A stone is dropped from a bridge and hits the ground after 4.0 seconds. How high is the cliff? y = ½ gt2 4.8m/s2 x 4.0s2 = 78.4m

12. A salmon jumps up a waterfall to return home to spawn. The waterfall is 2.0m high. What minimum speed must the fish meet to jump the waterfall? vf2 = vyo2 + 2a ∙ d = 6.26m/s

13. What is the resultant path of a ship traveling north at 8m/s if the tide is pushing at 2m/s east. What is the angle? 82m/s + 22m/s = √68m2/s2= 8.2m/s 8/2 tan-1 = 76°

14. A rock is dropped and hits bottom 5 seconds later. What is its velocity just before it hits bottom. vy = vyo + ayt 9.8m/s2 x 5 s = 49m/s What is the height of the cliff? y = ½ gt2 = 4.9m/s2 x 25 s2 = 122.5m

15. A rock is thrown from a cliff at 20m/s. What is the horizontal velocity after 2.0 seconds? 20m/s What is its vertical velocity in 2.0s? y = ayt 9.8m/s2 x 2.0 s = 19.8m/s

16. A rock is thrown from a cliff at 20m/s. What is its horizontal displacement after 3.0s? x = vxi t = 20m/s x 3.0s = 60m

17. A man shoots a gun at 2m above ground. The bullet is fired and hits the ground 1000m away. What vertical velocity did the bullet hit the ground? • vfy2 = voy2 + 2a x d • 2(9.8m/s2) x 2m = vfy2 • √39.2m2/s2 = 6.26m/s

18. A ball is projected horizontally from a point 245m above the ground. How long does it take to reach the ground? • y = ½ gt2 • t2 = y ÷ ½ g • 245m ÷ 4.9m/s2 = √50s2 • = 7.07 seconds

19. A ball is projected horizontally from a point 245m above the ground. How long does it take to reach the ground? = 7 seconds • If the ball strikes 49m horizontally from the point of projection, what is the horizontal velocity? • v = d/t 49m/7s = 7m/s

20. A projectile is shot upward at a 60° angle from the ground at 60m/s. What is the vertical component of velocity? • y = 60m/s (sin 60°) = 52m/s • What is its horizontal component of velocity? • vx= v (cosӨ) • vx = 60m/s (cos 60°) = 30m/s • How far in the x direction has it gone in 3 seconds? • x = vt 30m/s x 3 seconds = 90m

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