Question 22
A sky-diver falls vertically from a helicopter and
reaches constant (terminal) velocity. The graph shows the variation with time t
of the speed v
of the sky-diver.
Which graph
shows the variation with time t of the distance d fallen by the sky-diver?
Reference: Past Exam Paper – June 2018 Paper 12 Q7
Solution:
Answer:
C.
The speed of the sky-diver
increases at a decreasing rate until it becomes constant (where terminal
velocity is reached).
From a distance-time
graph, the speed may be obtained by the gradient of the graph.
So, in the distance-time
graph, the gradient should increase at a decreasing rate (a curve) and
then becomes constant and non-zero (a straight line, but not horizontal). [B
and D are incorrect]
From the velocity-time
graph of the sky-diver, initially the speed is zero. So, the gradient of the
distance-time graph should be zero initially (that is, the graph should be
horizontal initally). [C is correct]
Choice A cannot be correct because the non-zero gradient at time t = 0 shows a non-zero velocity. Only graph C has a zero velocity at time t = 0.
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