A net force acts on a body. Which characteristic of the body will definitely change?A. SpeedB. MomentumC. Kinetic energyD. Direction of motion

To determine which characteristic of a body will definitely change when a net force acts on it, let’s analyze each option:

1. Speed: The speed of the body may change if the net force is not zero. However, if the force is applied in a direction that does not affect the speed (for example, if it does not change the direction of the body’s movement), the speed may remain constant.

2. Momentum: The momentum of a body is defined as the product of its mass and its velocity. If a net force acts on the body, by Newton's second law (F = ma), the velocity will change, which means the momentum will also change.

3. Kinetic Energy: Kinetic energy (KE) is given by the formula $KE = \frac{1}{2} mv^2$. While a net force can lead to a change in kinetic energy, it is not guaranteed that kinetic energy will change. For instance, if the body moves at a constant speed but changes direction due to a force, the kinetic energy may remain the same.

4. Direction of motion: A net force will definitely change the direction of motion of the body unless the net force is applied directly in the direction of motion, resulting in a change in velocity.

Final Answer

The characteristic of the body that will definitely change is D. Direction of motion.