In order to increase muscular endurance, it is important to take part in activities that increase the size of muscle cells and the amount of blood that is delivered to the cells<span>. The increased size of the muscle cells reuires them to contract less to accomplish the same task; moreover, the increased blood flow helps deliver oxygen and nutrients to the blood.</span>
<span>A bike is compound machine.This means that it is made up of a bunch of different simple machines. Screws are used to hold the pieces together. The wheel of a bicycle is a wheel and axle. The pedals are also examples of this simple machine. The pedals are attached to a lever that turns a pulley.</span>
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50N is your force and the acceleration is -9.8m/s^2 due to gravity.
So, you just plug that in.

BUT you know that mass cannot be negative, so you just disregard the negative sign and the mass of the rock is 5.102 grams.