#### Transcript of PH 121 4.4-4.5

Relative Velocity & UCM

A boat can travel 2.30 m/s in still water.

If the boat points it prow directly across a stream whose current is 1.20 m/s what is the velocity of the boat relative to the shore?

What will be the position of the boat, relative to it point of origin after 3.00 s?

2.594 @ 27.55

V=2.59 m/s at 27.6 down stream

7.7826 x = 7.78 m

Uniform Circular Motion

What is the velocity of the ground based observer as

seen by the passenger on the train?

A. 9 m/s

B. -9 m/s

C. 11 m/s

D. -11 m/s

My new table saw blade has a

maximum rpm value 5300 rpm

What is the maximum value of

this saw blade in SI units?

Say I have been cutting now for about

10 minutes, how many radians have I gone

through, how many times has it gone around?

**Practice practice practice**

Me: 18, 19

You: 15, 20

"Could you explain the concept of converting a velocity from one vantage point to another?"

"Does uniform circular motion stay in the same place, same circle, or does it move in the shape of a spring?"

"Can you go over the difference between angular displacement and angular velocity?"

"Can you explain the example "Flying to Cleveland"? I didn't understand how they got the angle..."

"The only question I have is in regards to reference frames. On page 96 at the bottom of the page. Could you explain that formula?"

"how can free fall and projectile motion be the same?"

18) Susan driving north at 60 mph and Trent driving east at 45 mph are approaching an intersection. What is Trent's speed relative to Susan's reference frame?

15) A boat takes 3.0 hours to travel 30 km down a river, then 5.0 hours to return. how fast is the river flowing?

19) The picture sows the angular-position vs time graph for a particle moving in a circle what is the particles angular velocity at t = 1 , 4 , 7 seconds

20) The pictures shows the angular velocity vs time graph for a particle moving in a circle. how many revolutions does the object make during the first 4 s?

75 mph

2 km/hr

0, -pi/4 , 3 pi

9.55 rev.

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