From the top of a cliff, a person uses a slingshot to fire a pebble straight downward, which is the negative direction. The initial speed of the pebble is 9.0 m/s. (a) What is the acceleration (magnitude and direction) of the pebble during the downward motion? Is the pebble decelerating? Explain, (b) After 0.50 s, how far beneath tine cliff t

a) the acceleration is - 9.8 m/s^2 (gravity's acceleration), the magnitude is 9.8 m/s^2 and the direction is downwards.

The pebble is not decelerating since the magnitude of it's speed is increasing, even if it is on a negative direction.

b) after 0.5 s the pebble is 5.725 meters down. (or - 5.725m from it's initial position.)

Explanation:

a) the acceleration is given only by gravity, it's the only force acting on the pebble, the slingshot only gives the pebble an initial speed.

b) To calculate the position we use the equation

y0 + v0·t + ½·g·t² = yf

replacing:

0 + (-9.0m/s) * 0.5s + 1/2 (-9.8) * 0.5² = yf

-5.725 = yf