When an unbalanced (net) force acts on an object, which of the following statements about the object motion is correct?

Introduction / Context:
Newton laws of motion describe how forces affect the motion of objects. An important distinction is between balanced forces, which cancel each other and produce no change in motion, and unbalanced forces, which lead to acceleration. Understanding the effects of an unbalanced or net force on an object is fundamental to analysing everyday situations such as pushing a cart, braking a car, or changing direction while running. This question asks which description of the effect of an unbalanced force is correct.

Given Data / Assumptions:

• An unbalanced force means the net force on the object is not zero.
• Newton second law applies: net force equals mass times acceleration, F net = m * a.
• Options discuss change in motion, change in speed and direction, starting motion, and all of these.
• We assume a classical mechanics context without relativistic effects.

Concept / Approach:
According to Newton first law, an object at rest remains at rest and an object in motion continues in a straight line at constant speed unless acted upon by a net external force. Newton second law quantifies this by stating that an unbalanced force produces acceleration, which is any change in velocity. Velocity includes both speed and direction, so acceleration can mean speeding up, slowing down, or changing direction. Therefore, an unbalanced force can cause an object to start moving, speed up, slow down, or change direction. All of the individual effects listed in the options are possible outcomes of a net force, so the most complete statement is that all of the above can occur.

Step-by-Step Solution:
Step 1: Note that an unbalanced force implies F net is not zero, so there is a non zero acceleration a = F net / m. Step 2: Recognise that acceleration means a change in velocity, which covers changes in speed, direction, or both at once. Step 3: For an object initially at rest, a net force will produce a non zero acceleration, causing it to start moving. Step 4: For an object already in motion, a net force in the direction of motion will increase its speed, while a net force opposite to the motion will decrease its speed. Step 5: A net force at an angle to the current motion can change the direction of motion, as in circular motion where centripetal force keeps changing direction while speed remains nearly constant.

Verification / Alternative check:
Everyday examples confirm these principles. A stationary football starts moving when kicked because a net force acts on it. A moving car speeds up when the driver presses the accelerator, slows down when brakes are applied, and changes direction when the steering wheel is turned; all of these manoeuvres involve unbalanced forces. A planet in orbit around the Sun constantly changes direction due to gravitational force, even if its speed is nearly constant, illustrating change in velocity due to net force. These observations match the idea that an unbalanced force always causes some form of change in motion.

Why Other Options Are Wrong (individually incomplete):
It causes a change in the motion of the object: This is correct but general; it does not highlight the specific ways in which motion can change. It changes the speed and or direction of the object: Also correct, but still only part of the full description that includes starting motion from rest. It can cause an object at rest to start moving: Correct, but does not mention effects on objects already in motion.

Common Pitfalls:
Some learners think force is needed to keep an object moving at constant speed, which contradicts Newton first law. In fact, continuous force is only needed to overcome other forces like friction. Another mistake is to focus only on changes in speed and ignore changes in direction as real acceleration. Remember that any change in velocity, including direction only, indicates that an unbalanced force is acting. Therefore, the answer that includes all types of motion changes is the most accurate.

Final Answer:
When an unbalanced force acts on an object, all of the above effects can occur: it can change the object motion, alter its speed or direction, and even start motion from rest.