Forces and Motion

Cone and a Penny falling from a Cliff - (see previous page)
Calculations.

Q.  A cone falls from a cliff, how fast will it be moving after 3 seconds?

A.  Use   a = (v-u) ÷ t

a = 10 m/s2 because of gravity.
u = 0 (initial downward velocity).
t = 3

If you are good at maths,
you can rearrange the equation to give v-u = a x t.

v - 0 = 10 x 3
v = 30 m/s.
In reality, the velocity will be a little less than this
because air resistance (friction) will slow the cone  down.

You may have noticed that the above calculation
takes no account of the mass (or weight) of the cone.
All things fall with the same acceleration,
so if both a penny and a cone were thrown from a cliff at the same time,
they would both hit the ground at the same time.

Things will fall noticeably slower if
(i)  their density is close to the density of air
(for example a feather)
or (ii)  they have a large air resistance in proportion to their weight
(for example a parachute).

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