Question
If a constant force acts on a particle, its acceleration will:
  1. Remain constant.
  2. Gradually decrease.
  3. Gradually increase.
  4. Be undefined.

Answer

  1. Gradually decrease.
Explanation:
If a constant force is acting on a particle, the force will tend to accelerate the particle and increase its speed. But, due to increase in speed, the mass of the particle will increase by the relation $\text{m}=\frac{\text{m}_0}{\sqrt{1-\frac{\text{v}^2}{\text{c}^2}}}$
leading to decrease in acceleration as constant force is acting. Therefore, after sometime its acceleration will start decreasing gradually.

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