(a) (i) State the principle of superposition of waves. (ii) Distinguish between standing and stationary waves. (b) Define the following terms as applied to sound waves (i) Interference and beating. (ii) resonance and fundamental frequence.

4. Conjecture: Does thiction cause more energy to be wasted if the object is heavier? Why? Use the Gizmo to test this. Describe your results in your notebook or on a separate sheet.

Determina l'accelerazione di gravita g' esercitata dalla Terra sulla Luna, sapendo che la distanza della Luna dalla Terra è 60,25 raggi terrestri e che l'accelerazione di gravità g e \( 9,8 \mathrm{~m} / \mathrm{s}^{\mathrm{s}} \). Pensa come un ficico

A train moving in the east direction accelerates from rest to \( 36 \mathrm{~km} / \mathrm{h} \) in 20 s . What is the average acceleration during that time interval?

Which of the following sets of forces could not be in equilibrium? \( \begin{array}{ll}\text { (a) } 11,7,5 \text { newton. } & \text { (b) } 4,6,8 \text { newton. } \\ \text { (c) } 10,10,8 \text { newton. } & \text { (d) } 8,4,14 \text { newton. }\end{array} \)

2. For how long must a force of 10 N act on a body at rest of mass 400 grams for said body to reach a speed of \( 20 \mathrm{~m} / \mathrm{s} \) ?