A stone is projected from a point A on level ground with a speed of 20 ms $^{-1}$ at an angle of 30° to the horizontal, towards a pole standing 30 m away. Find the time, in seconds, at which the stone is level with the pole. Give your answer correct to 3 significant figures.

Model answer

1,73

Also accepted: 1.73, 1,732, 1.732, 1,7, 1.7

Explanation

There is no horizontal acceleration, so the horizontal distance is

x=20\cos30^{\circ}\,t=17,32t

. Setting

x=30

gives

t=\dfrac{30}{17,32}=1,73

Derived from ZIMSEC Mathematics 9164/4 Paper 4, November 2010, Q12

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