Final answer:
The net work done on a body pulled by a rope is not zero because work is defined as the product of force and displacement. A projectile has the same initial kinetic energy regardless of the angle of projection, but its maximum height depends on the vertical component of its velocity.
Step-by-step explanation:
The net work done on a body that is being pulled by a rope is not zero because the two forces involved act on different objects. Newton's 3rd law states that for every action, there is an equal and opposite reaction. When the body is pulled, the rope exerts a force on the body, causing it to accelerate. At the same time, the body exerts an equal and opposite force on the rope. However, the net work done on the body is not zero because work is defined as the product of force and displacement, and the body undergoes a displacement.
A projectile has the same initial kinetic energy regardless of the angle of projection because kinetic energy depends on the velocity of the object. As long as the speed of the projectile remains constant, the kinetic energy will be the same. However, the maximum height reached by the projectile will vary based on the angle of projection. This is because the vertical component of the velocity determines the projectile's vertical motion and affects its maximum height.
Learn more about Newton's 3rd law and projectile motion