When a body moves with a constant speed along a circle, then which of the following is correct :

Q. An object with a mass $10kg$ moves at a constant velocity of $10m/s$. A constant force then acts for $4second$ on the object and gives it a speed of $2m/s$ in opposite direction. The acceleration produced is:

Q. Consider the following statements
I) When a body is travelling with uniform speed, no force is acting on it.
II) When a body is travelling with constant velocity, no force is acting on it.
Which of the above statements is/are true?

Q. A body of mass $10\text{kg}$ is moving with a constant velocity $10\text{m/s}$. When a constant force acts for $4\text{s}$ on it, it moves with a velocity $2\text{m/s}$ in the opposite direction. The magnitude of force acting on the body is

Q. A body of mass $10\text{kg}$ is moving with a constant velocity $10\text{m/s}$. When a constant force acts for $4\text{s}$ on it, it moves with a velocity $2\text{m/s}$ in the opposite direction. The magnitude of force acting on the body is

Q. A body of mass m is moving in a circle of radius r with a constant speed $v$. If a force $\frac{m{v}^2}{r}$ is acting on the body towards the centre, then what will be the work done by this force in moving the body over half the circumference of the circle?