A small rocket is fired into the air from a fixed position on the ground - Leaving Cert Mathematics - Question Question - 2014
Question Question
A small rocket is fired into the air from a fixed position on the ground. Its flight lasts ten seconds. The height, in meters, of the rocket above the ground after t... show full transcript
Worked Solution & Example Answer:A small rocket is fired into the air from a fixed position on the ground - Leaving Cert Mathematics - Question Question - 2014
Step 1
Complete the table below.
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Answer
To complete the table, we will substitute the values of time (t) into the equation for height: h=10t−t2.
For t = 0:
h = 10(0) - (0)^2 = 0
For t = 1:
h = 10(1) - (1)^2 = 9
For t = 2:
h = 10(2) - (2)^2 = 16
For t = 3:
h = 10(3) - (3)^2 = 21
For t = 4:
h = 10(4) - (4)^2 = 24
For t = 5:
h = 10(5) - (5)^2 = 25
For t = 6:
h = 10(6) - (6)^2 = 24
For t = 7:
h = 10(7) - (7)^2 = 21
For t = 8:
h = 10(8) - (8)^2 = 16
For t = 9:
h = 10(9) - (9)^2 = 9
For t = 10:
h = 10(10) - (10)^2 = 0
The completed table is:
Time (t)
Height (h)
0
0
1
9
2
16
3
21
4
24
5
25
6
24
7
21
8
16
9
9
10
0
Step 2
Draw a graph to represent the height of the rocket during the ten seconds.
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Answer
To draw the graph, plot the points from the completed table on a grid, with the x-axis representing time (t) and the y-axis representing height (h). Connect the points with a smooth curve to reflect the trajectory of the rocket.
Step 3
Use your graph to estimate: (i) The height of the rocket after 2.5 seconds.
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Answer
From the graph, at t = 2.5 seconds, the height of the rocket is approximately 19 meters.
Step 4
Use your graph to estimate: (ii) The time when the rocket will again be at this height.
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Answer
The rocket will again be at this height of 19 meters at approximately 7.5 seconds.
Step 5
Use your graph to estimate: (iii) The co-ordinates of the highest point reached by the rocket.
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Answer
The highest point reached by the rocket is at the coordinates (5, 25), where 5 seconds is the time and 25 meters is the height.
Step 6
Find the slope of the line joining the points (6, 24) and (7, 21).
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The slope (m) of the line joining the points (6, 24) and (7, 21) is calculated using the formula: m=x2−x1y2−y1=7−621−24=1−3=−3.
Step 7
Would you expect the line joining the points (7, 21) and (8, 16) to be steeper than the line joining (6, 24) and (7, 21) or not? Give a reason for your answer.
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Yes, the line joining the points (7, 21) and (8, 16) is expected to be steeper because the absolute value of the slope is greater for this segment, calculated as: m=8−716−21=1−5=−5.
Step 8
Find $\frac{dh}{dt}$.
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To find the derivative of height with respect to time, we differentiate the height equation: dtdh=10−2t.
Step 9
Hence, find the maximum height reached by the rocket.
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To find the maximum height, set rac{dh}{dt} = 0: 10−2t=0⇒t=5.
Substituting t=5 into the height equation gives:
h = 10(5) - (5)^2 = 25 m.$$
Step 10
Find the speed of the rocket after 3 seconds.
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The speed of the rocket at t = 3 seconds is given by: S=dtdh=10−2(3)=4 m/s.
Step 11
Find the co-ordinates of the point at which the slope of the tangent is 2.
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To find the point where the slope is 2, we set the derivative equal to 2: 10−2t=2⇒2t=8⇒t=4.
Now, substituting t=4 into the height equation gives:
h = 10(4) - (4)^2 = 24.
Hence, the coordinates are (4, 24).
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