Answer
$$7\bar{0}\ kg \ m/s^2$$
Work Step by Step
We have
$$
\frac{(19 \ kg)(3.0 \ m/s)^2 }{ 2.46\ \ m}=69.512\ kg \ m/s^2
.$$
Now, round this product to two significant digits, which is the accuracy of the least accurate measurement. That is,
$$69.512\ kg \ m/s^2=7\bar{0}\ kg \ m/s^2$$
