Projectile Motion :D (1 Viewer)

[Smilebuffalo]

A horizontal drainpipe 6m above sea level empties stormwater into the sea. If the water comes out horizontally and reaches the sea 2m out from the pipe, find the initial velocity of the water, correct to 1 decimal place. let g = 10ms^-2 and neglect air resistance.

Answer = 1.8ms^-1

 

[untouchablecuz]

the angle is 90 because it is launched horizontally.

enjoy

 

[Michaelmoo]

the angle is 90 because it is launched horizontally.

enjoy

Um... doesn't horizontally mean the angle is 0?

and x(dot) should be vcos0? y(dot) should be vsin0? (when t = 0)

 

[clintmyster]

Um... doesn't horizontally mean the angle is 0?

yeah thats right, not 90

 

[Michaelmoo]

yeah thats right, not 90

Wait maybe he takes his angle relative to the vertical. Bit wierd though...

 

[untouchablecuz]

Um... doesn't horizontally mean the angle is 0?

and x(dot) should be vcos0? y(dot) should be vsin0? (when t = 0)

for these Q's, it take it from the vertical

and notice that y(dot) = vsin0 = vcos(90-0) = vcos90 and the same with x(dot)

 

[Smilebuffalo]

so should i be using the angle of projection = 0 or 90? :S

 

[Prashant Sallan]

so should i be using the angle of projection = 0 or 90? :S

works with both, bit what would be the angle if something is 'dropped' vertically down from a height?

 

[untouchablecuz]

no angle, all forces are already in the same vertical plane

there is only a gravitational force down (ignoring air resistance)

i.e F=mg => y(double dot) = g

If wind resistance is taken into account,

y(double dot) =g-R/m

 

[Smilebuffalo]

can someone please show me the entire method of solving this question using the angle = 0.

 

[tommykins]

 

[Michaelmoo]

for these Q's, it take it from the vertical

and notice that y(dot) = vsin0 = vcos(90-0) = vcos90 and the same with x(dot)

Just curious. Any particular reaason you take it relative to the vertical?

 

[untouchablecuz]

Just curious. Any particular reaason you take it relative to the vertical?

no patricular reason, it seems more logical

i've taught my self >90% of the 3 unit course and this has always been the way i've done it

tbh, i always thought everyone did it like me

 

[dw1999]

mate, when t=0,y=6, so y does not equal to gt^2/2, also you forgot to +c