Final answer:
The person expends 100 watts of power to move the crate by exerting a force of 50 Newtons over a distance of 8 meters in a time interval of 4 seconds.
Step-by-step explanation:
To calculate the power expended while exerting a force on an object, we can use the formula Power = Work done / Time taken. Work done is the product of the force applied and the distance over which it is applied, hence Work = Force × Distance. Given that a force of 50 Newtons is applied to move a crate 8 meters in 4 seconds, the work done can be calculated as 50 N × 8 m = 400 Joules. The power is then 400 J / 4 s = 100 Watts. Therefore, the person expends 100 watts of power to move the crate.