If a constant force is applied on an object in the same direction as its motion, what happens to the speed of the object over time?

Introduction / Context:
This question checks understanding of Newton second law of motion and the basic relationship between force, acceleration, and velocity. When a net force acts on an object in the direction of its motion, the object does not simply keep moving uniformly; rather, its speed changes with time. Recognising the effect of such a force is fundamental for solving many mechanics problems.

Given Data / Assumptions:
- A net force is applied on the object.- The direction of the force is the same as the direction of motion of the object.- We are considering motion in a straight line with no other significant opposing forces like friction.

Concept / Approach:
According to Newton second law, the net force F acting on a body of mass m produces an acceleration a given by the relation a = F / m. If the force and the velocity are in the same direction, this acceleration increases the magnitude of the velocity, that is, the speed. As long as the force continues to act and remains unbalanced, the speed keeps increasing. Only if the net force is zero will the object move with constant speed in a straight line, as stated by Newton first law.

Step-by-Step Solution:
1. Recognise that a non zero net force must cause an acceleration.2. Since the force is in the same direction as the motion, the acceleration is in the direction of the velocity vector.3. Acceleration in the direction of motion means that the speed increases with time.4. Therefore, the object gains kinetic energy and moves faster as long as the force acts.5. Conclude that the speed of the object increases, which matches the correct option.

Verification / Alternative check:
Consider pushing a trolley in a straight line. When you push it in the direction it is already moving, it speeds up. If you stop pushing, it eventually slows due to friction. This simple real life example shows that a force applied along the direction of motion increases speed, confirming the theoretical reasoning.

Why Other Options Are Wrong:
- It decreases: A decrease in speed would occur if the force acted opposite to the direction of motion, not in the same direction.- It becomes zero immediately: Speed does not become zero unless a strong opposing force stops the object; a forward force cannot make speed instantly zero.- It is not affected at all: This would violate Newton second law because a non zero net force must cause a change in motion.

Common Pitfalls:
Some learners confuse constant force with constant speed and think that if the force is steady, the motion is steady. Constant force actually produces constant acceleration, not constant speed. Forgetting this distinction leads to incorrect conclusions about how the speed changes.

Final Answer:
When a force is applied in the direction of motion, the speed of the object increases with time.