Quadratic Functions, Equations and Inequalities - Solving Quadratic Equations Graphically

Quadratic Functions, Equations and Inequalities - Solving Quadratic Equations Graphically

IP 2

Answer the whole of this question on a sheet of graph paper.

A ball is thrown from the top of a building.

Its vertical height \(h\), in metres, above the ground at time \(t\)seconds during the flight is represented by the equation \(h=20+5t-{{t}^{2}}\).

Some corresponding values of \(t\) and \(h\) are given in the table given.

\(t\)

\(0\)

\(1\)

\(2\)

\(3\)

\(4\)

\(5\)

\(6\)

\(7\)

\(h\)

\(20\)

\(24\)

\(26\)

\(p\)

\(24\)

\(20\)

\(14\)

\(6\)

  1. Calculate the value of \(p\).
  2. Using a scale of 2 cm to represent 1 unit, draw a horizontal \(t\)-axis for \(0\le t\le 8\).
    Using a scale of 1 cm to represent 2 unit, draw a vertical \(h\)-axis for \(0\le h\le 30\).
    On your axes, plot the points given in the table and join them with a smooth curve.
  3. Use your graph to estimate the
    1. maximum height of the ball from the ground,
    2. time when the ball is 18 m above the ground.
  4. Explain how you can use your graph to estimate the time when the ball hits the ground.

Solution:

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Answer:(a) \(p=26\) (b) Graph shown in working (c)(i) Approximately \(26.3\) m (ii) Approximately \(5.37\) s (d) Extend the curve to \(h=0\) and read \(t\approx7.62\) s.

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