A slingshot obeys Hooke's law and is used to launch pebbles vertically into the air. You observe that if you pull a pebble back 20 cm against the elastic band, the pebble goes 6 m high. Assuming that air drag is negligible, if you pull a pebble that is twice as heavy back 20 cm, how high will it go?
4 m
5 m
3 m
6 m

24 m

Explanation:

By applying the law of conservation of energy.

K.E = P.E

By rearrangement;

where;

k = spring constant

m = mass of pebble

h = height reached

x = stretched length

Since the drag force is negligible;

h = 24 m

air exerts forces on falling objects near earth’s surface.

explanation:

the term 'free falls' refer to object that are falling towards the earth, in a situation in which gravity is the only force acting on the object.

for an object in free fall, the acceleration is constant (g, the gravitational acceleration), and so the velocity of the object constantly increases.

for objects near earth's surface, there is always another force acting on the object: the resistance due to the air. this force is opposed to the direction of fall of the object, and it is proportional to the velocity of the object, so as the object falls down, this force increases up to a point when it balances the force of gravity, and the object continues its motion at constant velocity (called terminal velocity). since in this case gravity is not the only force acting on the object, we are not in a situation of free fall.