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Impossible Mechanics Question!

Question - Some of the year 13 students have moved into a position 7m above you on the balcony. They're about to launch pineapples horizontally a some annoying year 10s. You are 3m away from the year 13s

A - What is the minimum velocity the pineapples need in order to miss you?

B - The year 10s are 28m away from the year 13s. Calculate the initial velocity the pineapples need.

NEED HELP PLEASE !
Reply 1
Avatar for tom28
tom28
Original post by Ronnieee
Question - Some of the year 13 students have moved into a position 7m above you on the balcony. They're about to launch pineapples horizontally a some annoying year 10s. You are 3m away from the year 13s

A - What is the minimum velocity the pineapples need in order to miss you?

B - The year 10s are 28m away from the year 13s. Calculate the initial velocity the pineapples need.

NEED HELP PLEASE !


First one is a bit confusing, as in theory it could be 0, but I may have just misunderstood the question.

For part B, do suvat vertically to work out the time taken to fall 7m. Once you have the time, do suvat horizontally to work out the speed needed to travel 28m in the time you just worked out.
Reply 2
Avatar for Ronnieee
Ronnieee
OP
Original post by tom28
First one is a bit confusing, as in theory it could be 0, but I may have just misunderstood the question.

For part B, do suvat vertically to work out the time taken to fall 7m. Once you have the time, do suvat horizontally to work out the speed needed to travel 28m in the time you just worked out.



How? For part b :-

S = +7m
U = where do i get this from?
V = where do i get this from?
A = -9.81m/s
T = where do i get this from?

I need more than 2 numbers to so the calculations or am i missing something :confused:
Reply 3
Avatar for tom28
tom28
Original post by Ronnieee
How? For part b :-

S = +7m
U = where do i get this from?
V = where do i get this from?
A = -9.81m/s
T = where do i get this from?

I need more than 2 numbers to so the calculations or am i missing something :confused:


They are launched horizontally, so the initial vertical velocity = 0. If you are taking downwards as positive, then both displacement and acceleration will be positive.

so s=ut+0.5at^2, leaving you with a quadratic to solve.

Hope this helps.
Reply 4
Avatar for Ronnieee
Ronnieee
OP
Original post by tom28
They are launched horizontally, so the initial vertical velocity = 0. If you are taking downwards as positive, then both displacement and acceleration will be positive.

so s=ut+0.5at^2, leaving you with a quadratic to solve.

Hope this helps.



Oh yeah i meant to say :-
S = -7m
U = where do i get this from?
V = where do i get this from?
A = -9.81m/s
T = where do i get this from?

So your saying that if i launch horizontally the initial velocity will be zero all the time? Is this EVERY time for all horizontal launches?
Reply 5
Avatar for 117r
117r
9
What legend wrote this question?
Reply 6
Avatar for JOR2010
JOR2010
14
Original post by Ronnieee

Original post by Ronnieee
Question - Some of the year 13 students have moved into a position 7m above you on the balcony. They're about to launch pineapples horizontally a some annoying year 10s. You are 3m away from the year 13s

A - What is the minimum velocity the pineapples need in order to miss you?

B - The year 10s are 28m away from the year 13s. Calculate the initial velocity the pineapples need.

NEED HELP PLEASE !


A) not a question
B) not a question
Reply 7
Avatar for tom28
tom28
Original post by Ronnieee
Oh yeah i meant to say :-
S = -7m
U = where do i get this from?
V = where do i get this from?
A = -9.81m/s
T = where do i get this from?

So your saying that if i launch horizontally the initial velocity will be zero all the time? Is this EVERY time for all horizontal launches?


If it is launched horizontally, then initially it will only have a horizontal component of speed.
Reply 8
Avatar for raheem94
raheem94
13
You are 3m away from the year 13s Is 3m the horizontal displacement? If yes then the solution, according to me, is as follow:

Taking downwards as positive,
s = ut + 0.5at^2
7 = 0*t + 0.5*9.8*t^2
7 = 4.9t^2
t=1.195s

s=vt
3=v * 1.195
v = 2.5099...s ( initial velocity )
B - The year 10s are 28m away from the year 13s. Calculate the initial velocity the pineapples need.
Away horizontally or vertically or with an angle with the vertical/horizontal?
Untitled.png1.6KB
Reply 9
Avatar for Ronnieee
Ronnieee
OP
Original post by raheem94
You are 3m away from the year
s=vt
3=v * 1.195
v = 2.5099...s ( initial velocity )


The displacement is 7m not 3m
Reply 10
Avatar for Ronnieee
Ronnieee
OP
Original post by 117r
What legend wrote this question?



Lol... there are funnier questions on the sheet. A lot of naan bread throwing.
Reply 11
Avatar for raheem94
raheem94
13
Original post by Ronnieee
The displacement is 7m not 3m


7m is the vertical displacemet. I am asking you whether 3m is the horizontal displacement or the modulus of horizontal and vertical displacement?
Original post by Ronnieee

Original post by Ronnieee
Lol... there are funnier questions on the sheet. A lot of naan bread throwing.


Just out of interest, what are these other questions, and do they involve cheeseburgers and / or milkshakes?
Reply 13
Avatar for Ronnieee
Ronnieee
OP
Original post by raheem94
7m is the vertical displacemet. I am asking you whether 3m is the horizontal displacement or the modulus of horizontal and vertical displacement?


it is the horizontal displacement
surely you need to say how tall you are.
Reply 15
Avatar for raheem94
raheem94
13
Original post by Ronnieee
it is the horizontal displacement


So my answer to part 'a' will probably be correct.
What does 28m away in part 'b' tells, the horizontal or vertical displacement or the modulus of both?

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