Gerky children пелиетиленедые, Ukraine

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Physics 8th grade, Ed. S. V. Gromov. Problem #109

"A branch fell into the lake. A deer running by managed to notice that the wave created by the falling branch reached the shore in 10 seconds, and the distance between adjacent wave crests was equal to 10 cm, and in 2 seconds there were 4 splashes on the shore. Help the deer determine how far from the shore the branch fell."