Two clowns, Twinkle and Jingle, are throwing pies at each other. Twinkle throws a pie toward Jingle from 5 0 0 centimeters away. Its flight path is given by parametric equations { x y = = 1 0 0 t 8 0 t − 1 6 t 2 where t is time in seconds.
Two seconds later Jingle launches an interceptor pie from his location with the flight path { x y = = 5 0 0 − 5 0 0 ( t − 2 ) K ( t − 2 ) − 1 6 ( t − 2 ) 2 Find the value of K which will guarantee that the interceptor pie will hit its target (the pie thrown by Twinkle).
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I do not understand this at all
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The problem or solution?
They gave us paramatric equations for the position of each pie with respect to time. With exception of the equation containing K, choose any value for t and it will give you the (x, y) values representing the postion of the pie at that point in time.
For the pies to collied, their postion (x, y) not only have to be the same, but it has to happen at the same value for t .
Knowing this, you can set the equations for the x position of each pie and solve for t, to get the time when the pies collied.
The y postions have to also be equal at this point in time. So we set the equations for y equal to each other, and since we know the value for t we can substitule it into our expression.
After we do that, the only variable left is K, so we just solve the equality. The value that we get for K is the value that produces the y positions to be equal that point in time.
nice
Does Twinkle's pie going 2 seconds ahead make any differences?
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Yes it does. If you notice they gave us the parametric equations for Jingle's pie as (t-2). Essentially whenever we plug in a t value into the equations we are getting the position 2 seconds late. So if we plug in t = 2 => 2 - 2 = 0, and that ends up giving us the position at 0 seconds. which means the pie hasn't left Jingle's hand yet.
for can interceptor pie hit the pie thrown by Twinkle, need the two pies have same position in same time, so: { 1 0 0 t = 5 0 0 − 5 0 0 ( t − 2 ) 8 0 t − 1 6 t 2 = K ( t − 2 ) − 1 6 ( t − 2 ) 2
{ t = 5 / 2 8 0 ( 5 / 2 ) − 1 6 ( 5 / 2 ) 2 = K ( ( 5 / 2 ) − 2 ) − 1 6 ( ( 5 / 2 ) − 2 ) 2
so K = 2 0 8
Let us take the two equations considering x . We have x = 1 0 0 t and x = 5 0 0 − 5 0 0 ( t − 2 ) .
Substituting for x, we have 5 0 0 − 5 0 0 ( t − 2 ) = 1 0 0 t . We can then solve for t = 2 5 .
Now, we look at the two equations considering y. Plugging in t = 2 5 , we have
8 0 ( 2 5 ) − 1 6 ( 2 5 ) 2 = K ( 2 5 − 2 ) − 1 6 ( 2 5 − 2 ) 2 . 2 0 0 − 1 0 0 = K ( 2 1 ) − 1 6 ( 4 1 ) 1 0 0 = 2 K − 4
We can then simplify this down to 1 0 4 = 2 K , so we solve for K = 2 0 8 .
Great job!
The question can appear intimidating and scary, and I'm glad that you were able to approach it well.
awesome
For the two pies to meet at a point, the x & y co-ordinates must match after say t seconds. Hence, 100t = 500t - 500(t-2) giving t = 2.5 secs. Further, 80t - 16t^2 = K(t-2) -16(t-2)^2 where we plug in t = 2.5 to obtain K = 208
for make it more simple, jst compare the value of y from perametric eqn and thn solve for t..put value of t in eqn to get value of k..
Setting the two expressions for the x values equal gives us t=2.5 Now we can plug that into the expression for y to get y= K (0.5) -16 (0.25) which also equals $80t - 16t^2$, and we can solve for k.
the first equation is supposed as "A" the second the third and the fourth equation as supposed as B, C, D. now simulatneously solving the A & C eqaution gives the value of t which is = 5/2. now simulataneously solving equation B & D gives the value of k when we put the value of t from the above equation in it as 208. which is the required answer
the Solution x = x 100 t = 500 - 500(t-2) 600 t = 1500 t=2,5 s
y=y 0,5k= 100+4 k=104/0,5 k=208
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For the two pies to collied the x and y position have to be equal for the same time t .
First, find the time when the x positions are equal.
1 0 0 t = 5 0 0 − 5 0 0 ( t − 2 ) 1 0 0 t = 5 0 0 − 5 0 0 t + 1 0 0 0 1 0 0 t = 1 5 0 0 − 5 0 0 t 6 0 0 t = 1 5 0 0 t = 2 5
The y positions have to be equal for this t value, so we can replace t and solve for K .
8 0 t − 1 6 t 2 = K ( t − 2 ) − 1 6 ( t − 2 ) 2 8 0 ⋅ 2 5 − 1 6 ⋅ ( 2 5 ) 2 = K ( 2 5 − 2 ) − 1 6 ( 2 5 − 2 ) 2 1 0 0 = 2 1 K − 4 1 0 4 = 2 1 K K = 2 0 8