So,
We just have to recall Newton's three laws:
1. Objects at rest/in motion will remain at rest/stay in motion unless an external force acts upon the system.
2. The acceleration of an object is equal to the net force applied divided by the mass of the object.
3. For every action, there is an equal and opposite reaction.
Let's determine which statements are true.
1. Objects at rest will stay at rest
This is true as long as no outside force acts upon it.
2. Objects in motion will come to rest once force is removed
This is false because of the first law, which states that once force is removed, an object in motion will stay in motion.
3. Forces occur in pairs of equal magnitude and direction
This might look true except for the fact that the direction part of it is false. According to the third law, the reaction force is equal and opposite, not equal and collinear.
4. An increase in mass will cause a decrease in acceleration
This is true. According to the second law, since mass is in the denominator, an increase in mass will result in a decrease in acceleration for a given net force.
5. Acceleration is caused by unbalanced forces
Unbalanced forces is just another way of saying net force. The second law says that acceleration is directly proportional to net force. Therefore, unbalanced forces do cause acceleration.
The true statements are statements 1, 4, and 5.
