A rock fragment weighing 50N is displaced from the top of a cliff and falls 0.12 km to the ground. Calculate the kinetic energy (in J) of the rock just before it hits the ground. Assume air resistance is negligible.
Applying the law of conversation of energy, the gravitational potential energy (GPE) stored by the rock before falling is transformed into other types of energy as it falls. Without any external forces acting upon the object (i.e. negligible air resistance), this energy can be assumed to be converted to kinetic energy (KE). We cannot determine KE directly as we would need to know the velocity, which we do not have the means to calculate. Thus, we will calculate GPE for the rock at the top of the cliff and this value will be equal to the KE just before it hits the ground:GPE = mgh. -----> We are given 50N = mg = F , and thus the expression is simplified to Fh (more commonly recognised as Fd = work done). GPE = 50*120 = 6000 J Note: remember to convert to SI units! 0.12 kilometres = 120 metres
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