Explanation:
1. An object cannot remain at rest unless the net force exerted on it is zero. It is also known as the Newton's first law of motion. So, the correct option is (D).
2. If a block is moving to the left at a constant velocity, that means the velocity is same. So, the change in velocity is zero that is acceleration is zero. So, the net force exerted on the block is zero.
3. Mass of the block, m = 2 kg
Force experienced by the block, F = 4 N (towards right)
Since, the force is acting towards right.. So, the block will accelerates towards rest at the rate of 2 m/s². So, It must be moving to the right is the correct option.
4. A block is being pulled along a horizontal friction less surface by a constant horizontal force. Since, the force is constant, the acceleration will be constant. So, the block must be moving with a constant nonzero acceleration is the correct option.
Hence, this is the required solution.