Explain whether or not there must be an unbalanced net force acting on any moving object

No an unbalanced force only causes acceleration meaning an object can be moving but have balanced forces only the balanced forces would mean that the object would maintain a constant velocity instead of slowing down or speeding up

Answer: it will take   4.36 seconds to reach her average velocity 10.69 miles/hour.explanation:   we have equation of motion ,where s is the displacement, a is the acceleration, u is the initial velocity and t is the time taken.average velocity = displacement/ time taken.average velocity = 10.69 miles/hr = 10.69*1.6*1000/(60*60) = 4.75 m/s4.75 = s/ts = 4. 1we also have acceleration = 2.18 m/s², initial velocity = 0 m/sso it will take   4.36 seconds to reach her average velocity 10.69 miles/hour.

This is the answer: body 1 + engine 2