Final answer:
Line m can sometimes intersect plane r at a single point. Electric-field lines are unique at any given point, so only one can exist there. The graph of an object speeding up is not a straight line, and vectors can form right-angle triangles with their components. Option B is correct.
Step-by-step explanation:
The statement that line m intersects plane r at a single point could be sometimes true, specifically when line m is neither parallel to plane r nor contained within it. If line m were parallel to plane r or lay entirely within plane r, then it would either not intersect plane r at all, or intersect at infinite points (constituting a line). Hence, the correct answer is (b) Sometimes true.
In Physics, particularly when discussing electric fields, it's important to remember that only a single electric-field line can exist at any given point in space because electric field lines are meant to represent the direction of the electric field at a point, and at any point, the electric field has only one direction.
For the position vs time graph, an object speeding up would not have a graph of a straight line; instead, its graph would be curved, reflecting the change in speed over time. Therefore, the answer is (b) False.
When considering vector components, it is true that a vector can form the shape of a right-angle triangle with its x and y components, representing the horizontal and vertical components of the vector respectively.