A satellite dish is shaped like a paraboloid of revolution. The signals that emanate from a satellite strike the surface of the
dish and are reflected to a single point, where the receiver is located. If the dish is 14 feet across at its opening and 2 feet deep at its center, at what position should the receiver be placed?
1 answer:
Answer:
The receiver must be placed at a distance of 6.125 ft from the center.
Step-by-step explanation:
The dish is of parabola shape with the length of 14 feet and 2 feet deep from the center.
A parabola is a curve which is a set of all points in the plane which are at equal distance away from a given point called focus and given line called directrix.
We have to find out the point at which all the waves comes to one point where the receiver must be placed is the focus of the parabola.
The above scenario is shown in the image which can be converted in mathematical graphical representation of the parabolic curve.
The extreme two end points becomes, (-7,2) and (7,2)
The general equation for such parabola is:
x² = 4ay
where, a is the distance from the center and the focus.
Since, (7,2) satisfy the equation so,
7² = 4a×2
a = 49 /8
Thus,
<u>The receiver must be placed at a distance of 6.125 ft from the center.</u>
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Answer:
a) 40 feet
b) 54 ft/min
c) 4 mins
Step-by-step explanation:
Solution:-
- Kesha models the height ( h ) of the baton from the ground level but thrown from a platform of height hi.
- The function h ( t ) is modeled to follow a quadratic - parabolic path mathematically expressed as:
h ( t ) = −16t² + 54t + 40
Which gives the height of the baton from ground at time t mins.
- The initial point is of the height of the platform which is at a height of ( hi ) from the ground level.
- So the initial condition is expressed by time = 0 mins, the height of the baton h ( t ) would be:
h ( 0 ) = hi = -16*(0)^2 + 54*0 + 40
h ( 0 ) = hi = 0 + 0 + 40 = 40 feet
Answer: The height of the platform hi is 40 feet.
- The speed ( v ) during the parabolic path of the baton also varies with time t.
- The function of speed ( v ) with respect to time ( t ) can be determined by taking the derivative of displacement of baton from ground with respect to time t mins.
v ( t ) = dh / dt
v ( t )= d ( −16t² + 54t + 40 ) / dt
v ( t )= -2*(16)*t + 54
v ( t )= -32t + 54
- The velocity with which Kesha threw the baton is represented by tim t = 0 mins.
Hence,
v ( 0 ) = vi = -32*( 0 ) + 54
v ( 0 ) = vi = 54 ft / min
Answer: Kesha threw te baton with an initial speed of vo = 54 ft/min
- The baton reaches is maximum height h_max and comes down when all the kinetic energy is converted to potential energy. The baton starts to come down and cross the platform height hi = 40 feet and hits the ground.
- The height of the ball at ground is zero. Hence,
h ( t ) = 0
0 = −16t² + 54t + 40
0 = -8t^2 + 27t + 20
- Use the quadratic formula to solve the quadratic equation:
Answer: The time taken for the baton to hit the ground is t = 4 mins