Question

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A small coin of mass m is initially at rest. It is dropped from a height h above ground level.
The coin has a speed v as it hits the ground.
The gravitational field strength g is equal to 10N/kg.
(a) State an expression for:
• the gravitational potential energy of the coin at a height h above ground level
gravitational potential energy = .........................................................................................

• the kinetic energy of the coin when travelling at a speed v.
kinetic energy = .................................................................................................................[2] (b) The coin is dropped from the top of a building of height 380m.
Determine the speed of the coin as it hits the ground. You may ignore air resistance.

Answer 1

Explanation:

(a) The gravitational potential energy of the coin above the ground level is given by :

$E=mgh$

Where

m is mass of the object

g is acceleration

h is height

The kinetic energy of the coin when travelling at a speed v is given by :

$E_k=\dfrac{1}{2}mv^2$

(b) The coin is dropped from the top of a building of height 380m. Let v the speed of the coin as it hits the ground. Using the conservation of energy.

$v=\sqrt{2gh} \\\\v=\sqrt{2\times 9.8\times 390} \\\\v=87.42\ m/s$

Hence, this is the required solution.