IMAT 2018 Q55 [Velocity and Acceleration]

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An electric train is travelling on a straight, horizontal track. A constant resultant force (greater than zero) acts on the train in the direction of the train’s motion.

What happens to the magnitude of the acceleration and to the magnitude of the velocity of the train while this force is acting?

A. The acceleration increases and the velocity remains constant.
B. The acceleration remains constant and the velocity increases.
C. The acceleration decreases and the velocity increases.
D. The acceleration remains constant and the velocity remains constant.
E. The acceleration increases and the velocity increases.

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This question can simply be answered using Newton’s First Law of Motion:

F=ma

Where
F= Resultant Force
m= mass
a= acceleration

Using this formula we can see that acceleration and Resultant Force are Directly Proportional. This means that if we have a constant Resultant Force we must also have a constant acceleration.

Acceleration is the rate of change of velocity in an object with respect to time. Hence, if our acceleration is constant our velocity must be changing- or in turn here, increasing.

This makes our answer B.

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