A boy shouts towards a high wall 200m away. He hears his echo 0.25s after he hears his direct voice. Calculate the speed of sound.

The first sound travels directly from the Boy to the Girl, a distance of $200 \, \text{m}$, in $0.6 \, \text{s}$.

$$v = \frac{\text{Distance}}{\text{Time}}$$ $$v = \frac{200 \, \text{m}}{0.6 \, \text{s}}$$ $$v = \frac{1000}{3} \, \text{m/s} \approx 333.33 \, \text{m/s}$$

The second sound is heard $0.25 \, \text{s}$ after the first sound.

$$t_2 = t_1 + 0.25 \, \text{s}$$ $$t_2 = 0.6 \, \text{s} + 0.25 \, \text{s} = 0.85 \, \text{s}$$

$$L_2 = v \times t_2$$ $$L_2 = \frac{1000}{3} \, \text{m/s} \times 0.85 \, \text{s}$$ $$L_2 = \frac{850}{3} \, \text{m}$$ $$L_2 \approx 283.33 \, \text{m}$$

The length of the path followed by the second sound is $\boxed{\text{283.33 m}}$.

9. A person standing in an illuminated garden at night having two shadows of different sharpness indicates the presence of multiple light sources. Each light source casts its own shadow. If these light sources are of different sizes, intensities, or are positioned at different distances or angles from the person, they will produce shadows with varying degrees of umbra (darkest part) and penumbra (lighter, fuzzy part), leading to different sharpness.

10. When a positively charged metal sphere is brought near an uncharged metallic object, electrostatic induction occurs.

• The positive charge on the sphere attracts the free electrons in the uncharged metallic object towards the side closest to it. Therefore, point X will have an induced negative charge.
• This movement of electrons leaves a net positive charge on the side furthest from the sphere. Therefore, point Y will have an induced positive charge.