# AS Projectile motion problem

Discussion in 'Science' started by inneedoftea, Jan 22, 2016.

1. ### inneedofteaNew commenter

So,

Whilst doing a few end of topic questions with my class I came across the following problem ( Q7 page 78, Pearson textbook if you're interested):

A rock is dropped from a cliff of height 200m. At the same time an identical rock is launched horizontally from the top of the same cliff. Calculate:

1) Time taken for the rocks to hit the ground
2) The horizontal distance between them, when they hit the ground.

Part 1 is fine- straight forward SUVAT. Am I missing something on part 2? I don't see how it's possible without knowing the horizontal velocity (not given)!

Any help would be appreciated! Thanks

Horizontal distance does require the horizontal velocity.

3. ### SkeochStar commenter

It's a typo. Without the initial horizontal velocity it can't be done. You could tell the pupils a value to use - or you could leave it as it is and turn it into a useful discussion point in class.

4. ### JameslabtechNew commenter

Sounds a bit less fun than the monkey and the hunter experiment but using similar theory.

Show them the monkey and hunter experiment, its fun to do in class

5. ### rich_hodgettsNew commenter

If there is an answer to this question in the back of the textbook you could use it to work back to the value of velocity used by the person who wrote the book. This would also be a good bit of problem solving for your students to attempt.

6. ### OrionNew commenter

the secret with these is always to write two sets of S = U = V = etc.. down the page, add a subscript V or H

Next write 0 for anything which you know is zero and ? for anything you don't know.

Write all the formula out for V and H as they apply and simplify.

Then it is clearly not Physics any longer but a Maths puzzle.