118. Una molla di costante elastica \( K=100 \mathrm{~N} / \mathrm{m} \) è posta a un'estremità di un tubo in modo da farlo funzionare come un cannoncino. Il tubo si trova a un'altezza \( h=10 \mathrm{~m} \) rispetto al suolo e forma, con l'orizzontale, un angolo \( \alpha=30^{\circ} \). La molla viene compressa di 20 cm e spara una biglia di massa \( m=40 \mathrm{~g} \). Trascurando gli attriti, calcola: a) l'energia elastica liberata dalla molla; b) il massimo valore dell'energia potenziale gravitaziona- le riferita al suolo posseduta dalla biglia; c) I'energia cinetica con cui la biglia giunge al suolo.

7.2 A beam of light travels from water to plastic. The speed of light in plastic is \( 2,05 \times 10^{8} \mathrm{~m} \cdot \mathrm{~s}^{-1} \). The refractive index of water is 1,33 . Calculate the refractive index of plastic.

QUESTION 6 (Start on a new page.) It has been established that the planet Omega has a moon and that the moon of Omega orbits the planet at a height, above the surface of Omega, which is equal to twice the radius of Omega. The mass of planet Omega is \( 3 \times 10^{15} \mathrm{~kg} \) and the mass of its moon is \( 1.5 \times 10^{13} \mathrm{~kg} \). The radius of the planet Omega is \( 8.5 \times 10^{6} \mathrm{~m} \) and the radius of its moon is \( 2.5 \times 10^{5} \mathrm{~m} \). 6.1 Determine the distance between the centre of the planet Omega and the centre of its moon.

9. Si dejamos caer al suelo una piedra cuya masa es de 4 kg desde una altura de 4 m , ¿Cuál es la energía cinética cuando ya ha recorrido la mitad de la caída a) hacia el suelo? b) CCual es la velocidad cuando alcanza el suelo?

QUESTION 7 (Start on a new page.) 7.1 Reflection of light (and other forms of electromagnetic radiation) occurs when the waves meet a surface or other boundary that does not absorb the energy of the radiation and reflects the waves off the surface. Draw a fully labelled ray diagram to illustrate reflection.

A coil with an area of \( 0.6 \mathrm{~m}^{2} \) is held with its axis coinciding with the direction of a magnetic field (surface perpendicular to magnetic field), with a strength of 0.4 T . 8.3 Calculate the magnetic flux.