Question:
A truck of mass $M$ is moved under a force $F$. If the truck is then loaded with an object equal to the mass of the truck and the driving force is halved, then how does the acceleration change?
Solution:
Initial acceleration, $a_{1}=\frac{F}{M}$;
Final acceleration, $a_{2}=\frac{\mathrm{F} / 2}{2 \mathrm{M}}=\frac{\mathrm{F}}{4 \mathrm{M}}=\frac{a_{1}}{4}$.