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# LPH 105 W15 3.6-8

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## Richard Datwyler

on 28 April 2016

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#### Transcript of LPH 105 W15 3.6-8

Projectiles & Relative Velocity
A sailboat traveling with a speed of 4 knots heads directly up river against a 3 knot current. Its speed over ground is

A. 1 knot.
B. 7 knots.
C. 3 knots.
D. 5 knots.
A sailboat traveling with a speed of 4 knots heads directly down river with a 3 knot current. Its speed over ground is
A sailboat traveling with a speed of 4 knots heads directly across a river which has a 3 knot current. Its speed over ground is
A person decides to go jump off a cliff into a lake. The cliff is 7.0 m high, and he knows there are rocks at the base and needs to get at least 3.5 m out to be safe.
If he only jumps out horizontally, what speed does he need to be 'safe'?
2.9 m/s
A diver running 2.5 m/s dives out horizontally from the edge of a vertical cliff and 3.0 s later reaches the water below. How high was the cliff and how far from its base did the diver hit the water?
44 m
7.5 m
A ball thrown horizontally at 12.2 m/s from the roof of a building lands 21.0 m from the base of the building. How high is the building?
14.5 m
A football is kicked at ground level with a speed of 18.0 m/s at an angle of 31.0 to the horizontal. How much later does it hit the ground?
How far does it go?
1.89 s
29.2 m
A projectile is fired with an initial speed of 36.6 m/s at an angle of 42.2 degrees above the horizontal on a long flat firing range.
What is the max height reached?
The total time in air?
Range?
Speed of projectile 1.5 s after firing?
30.8 m
5.02 s
136 m
28.9 m/s
A swimmer is capable of swimming 0.60 m/s in still water. If she aims her body directly across a 45 m wide river whose current is 0.50 m/s how long will it take her to reach the other side? How far down stream will she land?
37.5 m
75 s

36.5 m/s
demonstrate

demonstrate

Practice
Practice
Practice
demonstrate

"I need help with questions like the ferry problem."
"The last question on the quiz 3.5-8 was really confusing. How do you find the magnitude of the vector using relative velocity?"
" I'm pretty lost still on how vectors relate to projectile motion. Can we go over that?"
A well seasoned ferry boat driver transports passengers across a river to a point on the opposite bank exactly opposite where they starts. The boat has an amazingly predictable top, and ONLY, speed of 3.49 m/s and the driver 'knows' by experience that the boat must point 35.0 degrees upstream to achieve this perpendicular path of travel. What must the uniform speed of the current in the river be?
On a large meadow you start at your camp and travel 357 m straight east and then turn 60.0 degrees south of east and walk another 125 m. What is your overall magnitude of your displacement from your camp?
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