Convert the following to the specified form: 4 rac12 kg to an improper fraction, the reciprocal of rac56, and 2.5 imes 103 J to ordinary form.

$$\frac{9}{2}$$

The improper fraction is $\boxed{\frac{9}{2} \text{ kg}}$.

:
To find the reciprocal of a fraction, we simply invert the fraction (swap the numerator and the denominator).

$$\text{Reciprocal of } \frac{5}{6} = \frac{6}{5}$$

The reciprocal is $\boxed{\frac{6}{5}}$.

:
To write $2.5 \times 10^3$ J in ordinary form, we move the decimal point to the right by the number of places indicated by the exponent of 10.

$$2.5 \times 10^3$$

The exponent is 3, so we move the decimal point 3 places to the right.

$$2.5 \to 2500$$

The ordinary form is $\boxed{2500 \text{ J}}$.