First, the hot air balloon went down (descended) 0.8 meters every second for 10 seconds. So, it's like:
0.8 meters/second × 10 seconds = 8 meters down
Then, it went up (climbed) 0.4 meters every second for 5 seconds. That's:
0.4 meters/second × 5 seconds = 2 meters up
Now, we need to find the total change in altitude. It went 8 meters down and then 2 meters up, so the total change is:
8 meters down - 2 meters up = 6 meters down
To find the average rate of change, we divide this total change (6 meters) by the total time (10 seconds + 5 seconds = 15 seconds). So, it's like:
6 meters ÷ 15 seconds = 0.4 meters per second down
So, the average rate of change in altitude is 0.4 meters per second downwards. Hope that helps!
