Final answer:
When moving a material cart on an inclined or declined surface, you must ensure that the component of the weight perpendicular to the slope is equal to the magnitude of the frictional force.
Step-by-step explanation:
When moving a material cart on an inclined or declined surface, you must be sure that the magnitude of the component of the weight perpendicular to the slope is equal to the magnitude of the frictional force. This is important because when these two forces are equal, the cart will not accelerate up or down the slope. If the component of the weight perpendicular to the slope is greater than the frictional force, the cart will accelerate downhill, and if it is smaller, the cart will accelerate uphill.