Answer
$1200N$
Work Step by Step
According to law of conservation of energy
$K.E_A+U_A=K.E_B+U_B$
$\implies \frac{1}{2}mv_A^2+mgy_A=\frac{1}{2}mv_B^2+0$
This simplifies to:
$v_B=\sqrt{v_A^2+2gy_A}$
We plug in the known values to obtain:
$v_B=\sqrt{(8.0)^2+2(9.81)(1.75)}=9.9\frac{m}{s}$
Now $\Sigma F_y=N-mg=\frac{mv^2}{r}$
This simplifies to:
$N=m(g+\frac{v^2}{r})$
We plug in the known values to obtain:
$N=(68)(9.81+\frac{9.9}{12})$
$N=1200N$
