1.when a train pulls a wagon, is the work zero because wagon pulls on the train with equal opposite force(newton's third law)?
2.what is negative net work and when it is done an on object, does it reduce objects kinetic energy?
3.if the work done on an object is zero, does either the force or the displacement HAVE to be zero in magnitude?
1. No The train does work; the wagon has work done on it.
2, Negative net work ON an object is work done BY that object against another force. When negative work is done ON an object, its kinetic energy may decrease, but not necessarily. The work done can be converted to other forms of energy.
3. No. They can be in perpendicular directions
Thanks one more question though.
When two identical masses are placed on frictionless slopes at identical heights. The first slope makes an angle of 30deg with respect to horizontal, second one with 40deg. Both balls are released simultananeously. At the bottom of the slope would the two balls have same speed because gravitational force is conserved?
Yes, in a frictionless situation such as you have described
1. When a train pulls a wagon, the work done is not zero. According to Newton's third law of motion, for every action, there is an equal and opposite reaction. In this case, when the wagon pulls on the train with an equal and opposite force, it does not mean that the work done is zero. Work is defined as the product of force and displacement, and even though the forces are equal and opposite, the displacements are not. The train moves forward, applying a force on the wagon, causing it to move as well. Therefore, work is being done on the wagon by the train, and vice versa.
2. Negative net work refers to the work done on an object in the opposite direction of its motion. When negative net work is done on an object, it decreases the object's kinetic energy. This means that the force acting on the object is opposing its motion, resulting in a reduction in the object's speed or velocity. The work-energy theorem states that the change in an object's kinetic energy is equal to the net work done on it, so when negative net work is done, it reduces the object's kinetic energy.
3. If the work done on an object is zero, it implies that either the force or the displacement (or both) can be zero in magnitude. The work done on an object is given by the formula: Work = Force * Displacement * cos(theta), where theta is the angle between the force and displacement vectors.
If the force is zero, then regardless of the magnitude of displacement, the work done will be zero. Similarly, if the displacement is zero, then regardless of the magnitude of force, the work done will be zero. It's important to note that the angle between the force and displacement vectors also plays a role. If the angle is 90 degrees (perpendicular), then the work done will be zero, even if both the force and displacement have magnitudes.