A person stands on top of a cliff and throws a ball with a speed of 20 m/s at an angle of 10 degrees from above the horizontal into the sea. What is the height of the cliff to 1 decimal place?
I would begin by instructing them to draw a diagram of the problem. This would be of a cliff, labelled height sy, with an arrow representing the ball being thrown from the top. This should be labelled with the velocity and angle of projection. I would then instruct them to choose a direction for the vertical and horizontal and thus split the problem into the two planes. Then, I would advise they write down what they know in terms of the variables of motion (i.e. x/y initial/final velocity, displacement, time, acceleration) which, in this case, is uy = 20sin10, ux=20cos10, ay=-9.8 ms-2 and tf=3s. Then, I would advise that they consider what variable they are looking for (sy) and to find the appropriate equation of motion that includes variables that we know or can calculate. Thus, they should find that the useful e.o.m. is s=ut+1/2at2 and thus obtain the final answer of 33.7m.
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