Q17 · 2023 · Technology-activeComplex familiar6 marks
QUESTION 17 (6 marks)
An object is projected upwards from ground level with an initial velocity of 15 m s at an angle of to the horizontal.
The object just passes over a drone hovering in the air. An observer is positioned directly below the drone and at a horizontal distance of 20 m from where the object is projected.
The observer commented that:
• it took the object around 2 to 2.5 seconds after its projection to reach the drone
• the object was still moving in an upwards direction as it passed the drone.
Assuming that air resistance is negligible, use a vector calculus approach to evaluate the reasonableness of the observer’s comments.
WORKED SOLUTION
6 marksQCAA guide · typeset solution
ANSWER
The first comment is reasonable; the second is not.
Worked solution
Taking upward as positive,
At horizontal displacement 20 m, s, so the first comment is reasonable. The maximum height occurs at about s, so at s the object is already moving downward; the second comment is not reasonable.
determines an expression for velocity
determines an expression for position
determines the time at which the object reaches the drone
determines the time at which the object reaches maximum height
evaluates both comments using mathematical reasoning
shows logical organisation communicating key steps
One QCAA sample method typeset for web; criterion wording is adapted from the official marking guide.
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