A bird flies at a speed of 15 m/s for 10s, 20 m/s for 20s, and 30 m/s for 15s. what is the birds average speed

Average speed = (total distance) / (total time)

First segment:

15 m/s for 10 sec;  distance covered = (15 x 10) = 150 m

Second segment:

20 m/s for 20 sec; distance covered = (20 x 20) = 400 m

Third segment:

30 m/s for 15 sec; distrance covered = (30 x 15) = 450 m

Total time = (10s + 20s + 15s) = 45 sec

Total distance = (150m + 400m + 450m) = 1,000 m (1 km)

Average speed = (1,000 m) / (45 sec) = 22.22 m/s

the part of the wave he is travelling on is the crest

grav forces affect all objects magnetic forces affect magnetic objects and electric currents