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A small rocket is fired into the air from a fixed position on the ground - Leaving Cert Mathematics - Question Question - 2014

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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=10tt2.h = 10t - t^2.

  • 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)
00
19
216
321
424
525
624
721
816
99
100

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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Answer

The slope (m) of the line joining the points (6, 24) and (7, 21) is calculated using the formula:
m=y2y1x2x1=212476=31=3.m = \frac{y_2 - y_1}{x_2 - x_1} = \frac{21 - 24}{7 - 6} = \frac{-3}{1} = -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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Answer

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=162187=51=5.m = \frac{16 - 21}{8 - 7} = \frac{-5}{1} = -5.

Step 8

Find $\frac{dh}{dt}$.

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Answer

To find the derivative of height with respect to time, we differentiate the height equation:
dhdt=102t.\frac{dh}{dt} = 10 - 2t.

Step 9

Hence, find the maximum height reached by the rocket.

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Answer

To find the maximum height, set rac{dh}{dt} = 0:
102t=0t=5.10 - 2t = 0 \Rightarrow t = 5.
Substituting t=5t = 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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Answer

The speed of the rocket at t = 3 seconds is given by:
S=dhdt=102(3)=4 m/s.S = \frac{dh}{dt} = 10 - 2(3) = 4 \text{ m/s}.

Step 11

Find the co-ordinates of the point at which the slope of the tangent is 2.

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Answer

To find the point where the slope is 2, we set the derivative equal to 2:
102t=22t=8t=4.10 - 2t = 2 \Rightarrow 2t = 8 \Rightarrow t = 4.
Now, substituting t=4t = 4 into the height equation gives:
h = 10(4) - (4)^2 = 24.
Hence, the coordinates are (4, 24).

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