Final answer:
The statement that both keys and splines prevent a part from turning on a shaft is true. (option A)
Step-by-step explanation:
Both keys and splines are designed to prevent a part from turning on a shaft, and this statement is True. They are mechanical features that ensure a non-rotational connection between a shaft and a mounted part.
Keys are typically inserted into matching keyways on both the shaft and the part being mounted, creating a solid connection that prevents rotation. Similarly, splines involve a series of ridges or teeth on a drive shaft that mesh with grooves in the mating piece, also preventing rotation and enabling torque to be transmitted.
The position vs time graph of an object that is speeding up is not a straight line; rather, it is typically curved, representing an increase in slope as the object's velocity increases. So, the statement is False.
The efficiency of a simple machine is always less than 100 percent due to some input work being converted to heat energy by friction; this statement is True.
Kinetic friction is often less than limiting static friction because there are fewer points of contact once an object is moving, and for this reason, it usually takes more force to start an object moving than to keep it in motion, making this statement True.