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March 29, 2024, 11:27:50 pm

Author Topic: Recreational Problems (Physics)  (Read 8871 times)  Share 

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zzdfa

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Re: Recreational Problems (Physics)
« Reply #30 on: July 02, 2009, 10:51:38 am »
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you are trapped in the centre of a circular pen, radius R.

there is a dog on the outside of the pen, it always runs towards the point on the fence that you are closest to.

The dog has a speed 4v, you have speed v. How can you reach the edge of the pen before the dog?

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Re: Recreational Problems (Physics)
« Reply #31 on: July 03, 2009, 03:01:45 pm »
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Let the pen have radius .

You have to run in a small circle around the middle post and then when the dog is exactly opposite for you, dash for the fence.

If you're running straight for the fence and want to just outrun the dog then you must leave a distance r from the circle, where:





However, as long as you keep within a radius of your angular velocity will be greater than the dog's, allowing you to position yourself opposite the dog.

So circle between and until the dog is opposite you, then run to the edge.

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Re: Recreational Problems (Physics)
« Reply #32 on: July 03, 2009, 03:33:50 pm »
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1. You are on a bumpy train ride, drinking mineral water out of a cylindrical cup. How much should you drink so that, after placing your beverage on a rattling table, it is most stable?

2. An astronaut in space turns on two flashlights simultaneously and pointing in opposite directions, sending out two beams that both move away from the astronaut at the speed of light. How fast does the front of one beam move away from the front of the other beam?

3. What is the shape of an object that has the greatest free-fall acceleration at a particular point on its surface?

4. Object A is moving at velocity and collides elastically with stationary object B, what is the greatest speed object B can have after the collision and why?
« Last Edit: July 04, 2009, 02:17:25 am by /0 »

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Re: Recreational Problems (Physics)
« Reply #33 on: August 07, 2009, 04:24:55 pm »
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A helicopter is hovering stationary above the ground. It has a propeller overhead of radius m that rotates with a frequency of Hz. A uniform magnetic field of strength T goes into the ground. Find the EMF between the edge of the propeller and the centre.

(Sorry fixed the problem: the helicopter is not moving)
« Last Edit: August 07, 2009, 04:27:13 pm by /0 »