12 - University Physics with Modern Physics

Question

(a) The recommended daily allowance (RDA) of the trace metal magnesium is 410 mg/day for males. Express this quantity in µg/day. (b) For adults, the RDA of the amino acid lysine is 12 mg per kg of body weight. How many grams per day should a 75-kg adult receive? (c) A typical multivitamin tablet can contain 2.0 mg of vitamin B2 (riboflavin), and the RDA is 0.0030 g/day. How many such tablets should a person take each day to get the proper amount of this vitamin, if he gets none from other sources? (d) The RDA for the trace element selenium is 0.000070 g/day. Express this dose in mg/day.

 

Step-by-Step Solution

Answer

(a) The given quantity in µg/day is 410000 µg/day.

(b) The required quantity for 75 kg person is 0.9 g.

(c) The required number of tablets is 1.5.

(d) The conversion in mg/day is 0.07 mg/day.

The conversion is µg/day

Part (a)

The conversion in µg/day is shown below,

$$\begin{gathered} 410 mg/day= 410\frac{mg}{day}\times \frac{1000 \mu g}{1 mg} \\ =410000 \mu g/day \end{gathered}$$

 

Thus, the given quantity in µg/day is 410000 µg/day.

Consumption of amino acid lysine

 

Part (b)

The amount of amino acid lysine for 75 kg person can be calculated as,

$$\begin{gathered} =12\frac{mg}{kg}\times \frac{1g}{1000 mg}\times 75 kg \\ =0.9 g \end{gathered}$$

 Thus, the required quantity for 75 kg person is 0.9 g.

Calculation of number of tablets

Part (c)

The number of tablets can be calculated as,

$$\begin{gathered} \frac{0.003 {\displaystyle \frac{g}{day}}}{2 {\displaystyle \frac{mg}{day}}\times {\displaystyle \frac{1 g}{1000 mg}}} \\ =1.5 \end{gathered}$$

 

Thus, the required number of tablets is 1.5.

The conversion in mg/day

The conversion in mg/day is shown below,

$$\begin{gathered} 0.000070 g/day=0.000070 \frac{g}{day}\times \frac{1000 mg}{1 g} \\ =0.07 mg/day \end{gathered}$$

 

Thus, the conversion in mg/day is 0.07 mg/day.