Theo định luật bảo toàn cơ năng:

`W_A=W_B`

`<=>` `1/{2}mv_A^2+gmh=1/{2}mv_B^2`

`<=>` `1/{2}m.5^2+10m.40=1/{2}mv_B^2`

`<=>` `12,5m+400m=1/{2}mv_B^2`

`<=>` `412,5=1/{2}v_B^2`

`=>` `v_B^2={412,5}/{1/2}=825`

`=>` `v_B=5\sqrt{33}`m/s

gọi:
+A điểm ném
+B điểm chạm đất
bảo toàn cơ năng:
`W_A=W_B`
`<=> 1/2m5^2+m.40.10=1/2mv_B^2`
`<=>v_B=5sqrt(33)`(m/s)

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