Video Transcript
An object accelerates uniformly,
increasing its speed. The object then travels at a
constant speed. Finally, the object accelerates
uniformly in the opposite direction to its initial acceleration, decreasing its
speed. In which part of the motion of the
object did the object have a constant value of acceleration? Is it (A) the acceleration had a
constant value only when the speed of the object was increasing? (B) The acceleration had a constant
value only when the speed of the object was decreasing. (C) For each part of the motion,
the acceleration had constant values. (D) The acceleration had a constant
value only when the speed of the object was constant. Or (E) the acceleration had a
constant value for the whole of the motion, not for a specific part of the
motion.
After clearing some space, let us
consider the different parts of the motion of the object. In the first part of the motion,
the object accelerates uniformly, increasing its speed. Secondly, the object travels at a
constant speed. Finally, the object accelerates
uniformly in the opposite direction to its initial acceleration, decreasing its
speed.
We see that in part one and part
three of the motion, the object accelerates uniformly. This means that in part one and
part three, the acceleration of the object had a constant value. But what about part two? Does the acceleration in part two
of the motion have a constant value? The question states that the object
traveled at a constant speed in part two of the motion. This means that the object had zero
acceleration in part two of the motion. As the acceleration was zero, the
acceleration did not change in part two of the motion. And as it did not change, it had a
constant value, which was zero.
So we can see that the acceleration
had a constant value in all three parts of the motion. The constant value in part two of
the motion was a different value to the constant values in part one and in part
three. But in all three parts, the
accelerations of the object had constant values.
Option (C) states “For each part of
the motion, the acceleration had constant values.” Therefore, option (C) is correct,
and all the other options are incorrect.
