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March 29, 2024, 01:07:14 pm

Author Topic: Rishi's Physics Thread  (Read 14080 times)  Share 

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Rishi97

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Re: Rishi's Physics Thread
« Reply #30 on: April 09, 2014, 01:00:09 pm »
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What is a transistor?
I've never heard of it and didn't think it was important but it's coming up a lot in the textbook
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RKTR

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Re: Rishi's Physics Thread
« Reply #31 on: April 09, 2014, 04:12:58 pm »
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A portable electric heater has the two settings, 'high' and 'low'. These heating levels are obtained by connecting two heating elements either in series or in parallel, across the 240-VRMS mains supply. Each element has the same electrical resistance. When the heating elements are connected in series, the total power dissipated in them is 960W.

a) WHat is the resistance of each element?
I used the formula P=V2/ R and found the R value to be 60 ohms. But since there are 2 elements, would I divide the 60 or multiply it?

Thanks

since R in series = R1 + R2
and you know R1=R2
R=2R1
to get R1 , you divide R by 2
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Rishi97

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Re: Rishi's Physics Thread
« Reply #32 on: April 09, 2014, 04:30:05 pm »
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since R in series = R1 + R2
and you know R1=R2
R=2R1
to get R1 , you divide R by 2

Oh ok, so you divide. Thanks RKTR
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Rishi97

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Re: Rishi's Physics Thread
« Reply #33 on: April 16, 2014, 04:12:01 pm »
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A physics class conducting a research project on projectile motion constructs a device that can launch a cricket ball. The launching device is designed so that the ball can be launched at ground level with an initial velocity of 28m/s at an angle of 30 degrees to the horizontal.
a) Calculate the vertical component of the velocity of the ball after 2.0s .
Thanks
« Last Edit: April 16, 2014, 04:14:22 pm by Rishi97 »
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Stevensmay

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Re: Rishi's Physics Thread
« Reply #34 on: April 16, 2014, 04:31:36 pm »
+1
So we are given , but we need to find , the initial vertical velocity.

Using the angle given we get that

We can now apply our equations for constant acceleration in one dimension, as we have isolated the direction (vertical) we are interested in.
Simplest way to do this is with where




When t=2, the vertical component of velocity will be -5.6m/s (toward the ground).

Rishi97

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Re: Rishi's Physics Thread
« Reply #35 on: April 16, 2014, 04:33:35 pm »
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Thanks a million :)
But why are we assuming 9.8 is negative?
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Stevensmay

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Re: Rishi's Physics Thread
« Reply #36 on: April 16, 2014, 04:39:00 pm »
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Not really assuming, more of just arbitrarily deciding. I just decided that up would be away from earth.

If we define going away from the earth to be positive, then if gravity is pulling it back to earth gravity must be negative.

I could have just as easily said that going towards the earth is positive, made gravity positive but then made the initial velocity negative instead.

Rishi97

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Re: Rishi's Physics Thread
« Reply #37 on: April 17, 2014, 07:32:28 pm »
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A speeding motorbike travels past a stationary police car at a speed of 35 m/s . The police car starts accelerating immediately at 4 m/s/s, and keeps accelerating at this rate until it has passed the bike.
1) How far does the police car travel before it overtakes the motorbike?
2) At what time does the police car overtake the motorbike?

I have no idea whatsoever...
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Conic

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Re: Rishi's Physics Thread
« Reply #38 on: April 17, 2014, 09:36:19 pm »
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The distance travelled by the car is (because it is not accelerating). The distance travelled by the police car is (As it starts from rest).
When the distances are the same:



So the police car catches up after 17.5s. The distance is the same for both, so we can get the distance using the formula for the car:



So the police car travels 612.5m before it catches up.
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Rishi97

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Re: Rishi's Physics Thread
« Reply #39 on: April 19, 2014, 03:11:39 pm »
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The law of conservation of momentum applies in isolated systems. What is meant by isolated systems?
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Re: Rishi's Physics Thread
« Reply #40 on: April 19, 2014, 03:36:02 pm »
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There are no external forces acting on the system (e.g. drag, friction etc).
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Rod

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Re: Rishi's Physics Thread
« Reply #41 on: April 19, 2014, 03:39:29 pm »
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Hey Rishi :)

Isolated systems are ones that only involve INTERNAL forces. So for example, forces only between objects in the collision. No external forces.
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Rishi97

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Re: Rishi's Physics Thread
« Reply #42 on: April 19, 2014, 03:42:53 pm »
+1
Hey Rishi :)

Isolated systems are ones that only involve INTERNAL forces. So for example, forces only between objects in the collision. No external forces.

Thanks heaps Rod :)
I'll add it to my notes right now
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Re: Rishi's Physics Thread
« Reply #43 on: April 20, 2014, 02:09:49 pm »
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Kermit Cookie rides his polo pony in a very tight circle, of radius 5m. The friction force between the pony's hooves and the ground cannot exceed 8000N. The mass of the pony and Kermit is 400kg.
What is the maximum speed they can achieve during this turn?

Thanks in advance ;D
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Yacoubb

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Re: Rishi's Physics Thread
« Reply #44 on: April 20, 2014, 04:16:47 pm »
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Kermit Cookie rides his polo pony in a very tight circle, of radius 5m. The friction force between the pony's hooves and the ground cannot exceed 8000N. The mass of the pony and Kermit is 400kg.
What is the maximum speed they can achieve during this turn?

Thanks in advance ;D

If the frictional force cannot exceed 8000N, then the centripetal force = 8000N

F = mv^2 / r
8000 * 5 = 400 * v^2
v^2 = 100
v = 10m/s

Is the answer right? That's what I got anyway