Bài 4.113
a.
• wA = wB
<=> wđA + wtA = wđB + wtB
<=> mgzA = 12,5
<=> 0,25.10.zA = 12,5
=> zA = 5 (m)
• wđB = $\frac{1}{2}$m$vB^2$
=> 12,5 = $\frac{1}{2}$.0,25.$vB^2$
=> vB = 10 m/s
b.
wB = wC
<=> 12,5 = wđC + wtC = wdD + wdD
<=> 12,5 = 2.$\frac{1}{2}$m$vC^2$
<=> 12,5 = 0,25$vC^2$
=> vC = 5√2 m/s
c.
wB = wD
<=> 12,5 = wdD + wtD = 2wtD + wtD
<=> 12,5 = 3mgzD
<=> 12,5 = 3.0,25.10.zD
=> zD = 1,6m
Bài 4.114
a.
wA = wđA + wtA = $\frac{1}{2}$m$vA^2$
<=> wA = $\frac{1}{2}$.$20^2$
=> wA = 200 J
b.
wA = wB
<=> 200 = wđB + wtB = mgzB
<=> 200 = 10.zB
=> zB = 20m
c.
Vmax khi h=0
=> Vmax = 20m/s
