## ΒΑΡΥΤΗΤΑ ΚΑΙ ΕΠΙΤΑΧΥΝΣΗ

Απευθύνεται σε μαθήτριες και μαθητές του Λυκείου,Πραγματεύεται τις κοινές διαπιστώσεις παρατηρητή όταν βρεθεί μέσα σε κινούμενο ανελκυστήρα ή μέσα σε βαρυτικό πεδίο.

## Πέμπτη 6 Δεκεμβρίου 2012

### Stone projected upwards from a cliff.

A stone is projected almost vertically upwards at 20 ms−1 from the edge of a cliff as shown. It
finally lands on the ground at the base of the cliff. The sequence diagram below shows the position
of the stone at one-second intervals. Image 0 is just after projection, and Image 5 is just before
landing. Gravitational acceleration is taken as 10 ms−2 and air resistance is ignored.

(a) State whether the stone’s acceleration is upward, downward or zero in each of the following
cases:
(i) when the stone is on its way up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
(ii) when the stone is on its way down . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
(iii) when the stone is at the top of its path . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

(b) Next to each of the six images draw in a vector to represent the instantaneous velocity at
that stage of the motion. The vector at image 0 has been drawn in for you. Pay attention to
the direction and relative lengths of the vectors, and label them with their magnitudes in ms−1 .

(c) Draw a velocity–time graph to represent the motion of the stone. On the graph label the
stages representing upwards motion and downwards motion, and label the topmost point
of the motion.

(d) What does the gradient of the graph represent?

(e) Determine the height of the cliff.