Suppose you are a basketball player with a height of 2 meters, currently practicing in a basketball court. You want to shoot the ball into the ring, which is 5 meters high and 6 meters away from you, with initial speed 5 m/s at an angle of θ degrees with the horizontal.
Is there any possible value of θ that makes the ball enter the ring?
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Let's identify the given:
I used where the basketball player is standing as the reference point (origin).
r i = 2 j ^ r f = 6 i ^ + 5 j ^ ∣ V ∣ = 5 m/s a = − 9 . 8 j ^
Then, we will use this 2 formulas:
V = V o x i ^ + V o y j ^
and
r f = r i + V t + 0 . 5 a t 2
V = V o x i ^ + V o y j ^ = 5 cos θ i ^ + 5 sin θ j ^
r f ⟹ 6 i ^ + 5 j ^ = r i + V t + 0 . 5 a t 2 = 2 j ^ + ( 5 cos θ i ^ + 5 sin θ j ^ ) t − 4 . 9 t 2 j ^
By analogy,
6 = 5 t cos θ ⟹ t = 5 cos θ 6
and
5 3 7 5 cos 2 θ 7 5 cos 2 θ ( 7 5 cos 2 θ + 4 . 9 ( 3 6 ) ) 2 2 8 1 2 5 a 2 + 3 9 6 0 a + 3 1 1 1 7 = 2 + 5 t sin θ − 4 . 9 t 2 = 5 ( 5 cos θ 6 ) ( sin θ ) − 4 . 9 ( 5 cos θ 6 ) 2 = 1 5 0 sin θ cos θ − 4 . 9 ( 3 6 ) = 1 5 0 ( 1 − cos 2 θ ) cos θ − 4 . 9 ( 3 6 ) = 1 5 0 2 ( 1 − cos 2 θ ) ( cos 2 θ ) = 0 a = cos 2 θ ; a ≤ 1
If you get the discriminant of that quadratic equation, you'll see that a is imaginary, hence, there is NO such θ applicable.
would you, please, be able to use any drawings or graphics to show the cos and sin? I am sort of confused about how the sum of the initial velocities for the basis vectors is 5 cos(theta)i + 5 sin(theta)j
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I will try my best to add picture on my solution as soon as possible. I can't do it right now cause I am just a little bit busy. XD
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that would be really cool. I would be interested to see it.
Thanks
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@Matthew Agona – I think, illustrations might not help so, I'll just explain it:
The vector V ( velocity ) can be express as V = V o x i ^ + V o y j ^ .
It is by definition/convenience that V o x (x - component of the velocity) is equal to ∣ V ∣ cos θ
Why cos ? Remember that in trigonometry, usually, cosines are interconnected to the value of abscissa.
Meanwhile, V o y = ∣ V ∣ sin θ . Meanwhile, sines are interconnected to the value of ordinate.
I hope this explanation somehow enlighten you. I can't even explain this things properly. :( Sorry about that.
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The highest the basketball player can throw the ball will be if he threw it at a 90 degree angle (straight up) With an initial velocity of 5 m/s, the highest the ball will go is 1.27 meters above his initial height of 2 m. Therefore, the maximum height of the ball, above ground, is 3.27 meters, which is lower than the hoop height of 5 meters. So, the answer is no.