2. STEM Density is measured in units of mass per unit of volume. It can be thought of as a unit rate. The mass of a block of aluminum is 9.45 grams. The volume is 3.5 cubic centimeters \( \left(\mathrm{cm}^{3}\right) \). What is the density of the aluminum?

6. In Activity 12 , if you pull down on the DRFS sensor arm, the DRFS produces a positive reading. How can one justify the statement that the DRFS takes \( u p \) to be the positive direction for the force the spring applies to the mass? (The correct answer uses Newton's Third Law but not \( F=-k y \).)

Look at the electrical diagram. \begin{tabular}{l}\( V=8.6 \mathrm{~V} \) \\ \( I 1=0.3 \mathrm{~A} \) \\ \( I 2=0.5 \mathrm{~A} \) \\ \( I 3=0.2 \mathrm{~A} \) \\ Calculate the total resistance. \\ \hline 8.6 \\ \hline OK. \\ \( \begin{array}{l}V=10.6 \mathrm{~V} \\ I 1=0.9 \mathrm{~A} \\ I 2=0.3 \mathrm{~A} \\ I 3=0.3 \mathrm{~A}\end{array} \) \\ Calculate the total resistance. \\ \hline\end{tabular}

11.2 มวล \( \mathrm{m}=200 \mathrm{~kg}, \mathrm{a}=5.0 \mathrm{~m} / \mathrm{s}^{2} \)

81 point Heavy but sensitive equipment (like hifi equipment), often have spring-loaded legs to dampen external vibrations. Consider an amplifier of mass 29.5 kg resting on a flat table. The amplifier has 4 feet, each consisting of identical springs of spring constant \( 16.4 \times 10^{3} \mathrm{~N} / \mathrm{m} \). By how much (in mm) are each of the springs in the feet compressed?

Ex 26 (Pec9) จากรูป นำเชือกผูกกับก้อนน้ำหนัก \( W \) จงหาอัตราส่วนของขนาดของแรงดึงในเส้นเชือก \( T_{1} \) ต่อ \( T_{2} \) กำหนด \( \sin 53^{\circ}=4 / 5, \sin 37^{\circ}=3 / 5 \)