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## #1 2005-09-18 01:29:46

Jaswahhihi
Member
Registered: 2005-07-23
Posts: 11

### Mechanics 2!!

darn I hate this question! Theres no diagram but Ill copy the question out. Oh and the topics Parbolic motion.

A particle is projected at a speed of 45ms at an angle of 30 degrees above the horizontal.

(a) Calculate
(i) the speed and direction of the motion of the particle after 4 seconds,
(ii) the maximum height above the point of projection reached by the particle.

I can do (b) but the first two are the ones that got me. Anyhoo the answers are:

(a)
(i) 42.4 ms at 23.2 degrees below the horizontal
(ii) 25.8 m

98% of the teenage population does or has tried smoking pot. If you're one of the 2% who hasn't, copy & paste this into your signature.

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## #2 2005-09-18 04:57:34

kylekatarn
Member
Registered: 2005-07-24
Posts: 445

### Re: Mechanics 2!!

should we consider

or

Last edited by kylekatarn (2005-09-18 05:04:06)

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## #3 2005-09-18 05:18:13

kylekatarn
Member
Registered: 2005-07-24
Posts: 445

### Re: Mechanics 2!!

consider the gravity constant g = - 9.81

*Initial conditions (t = 0 s) *

lets find the initial speed components vx and vy

i) Speed and Angle @ t=4s
the x component doesn't change

the y component changes because of gravity

Speed is a vector, not a scalar.

You probably want the norm...

Now finding the angle is easy.:

θ = -23.2º means 23.2º below horizontal

ii) Finding the maximum height

we need to find the time corresponding to that moment -

since:

and

plug this value in the y(t) equation and find the max height.

And that's it!

Last edited by kylekatarn (2005-09-18 06:16:41)

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## #4 2005-09-18 05:57:44

Jaswahhihi
Member
Registered: 2005-07-23
Posts: 11

### Re: Mechanics 2!!

Sorry mate, while I was waiting for a reply I worked it out. And its just 9.8. Thanks though

98% of the teenage population does or has tried smoking pot. If you're one of the 2% who hasn't, copy & paste this into your signature.

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## #5 2005-09-18 06:16:15

kylekatarn
Member
Registered: 2005-07-24
Posts: 445

### Re: Mechanics 2!!

lol. I was working on the solution so I left the post open for a while...
I must type faster next time : ) Writing the solution in latex takes longer than actually solving it. lolol

Anyway, it was great to work on physics again!

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