Final answer:
To find the time and average speed for an airplane's journey, use the formula Average speed = Total distance / Total time. Option b, with a time of 4 hours and an average speed of 100 km/hr, correctly represents the airplane completing a 400 km journey.
Step-by-step explanation:
To calculate the time and average speed of an airplane completing a 400 km journey with two different speeds, one can use the formula for average speed:
Average speed (Vavg) = Total distance / Total time
If we look at option b, the total time given is 4 hours, and the average speed is given as 100 km/hr. Plugging these into the formula would yield:
100 km/hr = 400 km / 4 hours
This is true since 100 km/hr multiplied by 4 hours equals 400 km, so option b is correct.
Let's check option a as an example:
If the average speed were 171.43 km/hr for 2.33 hours, the distance covered would be:
171.43 km/hr * 2.33 hours = 399.73 km, which is close but not precisely 400 km. Therefore, option b is the correct answer.
It's important to note that for a round trip where the displacement is zero, such as going to the store and back, the average velocity would be zero, but the average speed is the total distance divided by the total time, regardless of direction.