Two identical 9.60-g metal spheres (small enough to be treated as particles) are hung from separate 500-mm strings attached to the same nail in a ceiling. Surplus electrons are added to each sphere, and then the spheres are brought in contact with each other and released. Their equilibrium position is such that each string makes a 17.0 ∘ angle with the vertical. How many surplus electrons are on each sphere?

1.349 × 10¹² electrons

Explanation:

At equilibrium, the tension T in the string is resolved into horizontal and vertical components. Tcos17 being the vertical component and Tsin17 the horizontal component. The electrostatic force of repulsion at equilibrium, F = kq²/r² where q = excess charge on sphere and r = distance apart at equilibrium,F acts horizontally to the left and its weight, mg acts vertically downwards.

For equilibrium, sum of horizontal components = 0 and  sum of horizontal components = 0. So, Tsin17 - F = 0

Tsin17 = F ⇒ Tsin17 = kq²/r² (1)

Also Tcos17 - mg = 0  ⇒ Tcos17 = mg (2)

Dividing (1) by (2), we have

Tsin17/Tcos17 = kq²/r² ÷ mg

tan17 = kq²/mgr²

q = r√(mgtan17/k)

We find r using cosine rule r = √(500² + 500² -2 × 500²cos 2 × 17) since the string and the masses form an isosceles triangle at equilibrium.

r = √(2 × 500² -2 × 500²cos34) = 500√2(1 - cos 34) = 500√2 × 0.1710 =120.89 mm = 0.1209 m

substituting m = 9.60 g = 9.6 × 10⁻³ g, k = 9 × 10⁹ Nm²/C² and r into q, we have,

q = r√(mgtan17/k)

  = 0.1209 m√(9.6 × 10⁻³ g × 9.8 m/s² × tan17/9 × 10⁹ Nm²/C²)

  = 0.1209 m√(28.76 × 10⁻³ N/9 × 10⁹ Nm²/C²)

  =  0.1209 m√(3.195 × 10⁻¹² C²/m²)

  =  0.1209 m × 1.7877 × 10⁻⁶ C/m

  = 0.2161 × 10⁻⁶ C

  = 2.161 × 10⁻⁷ C

To find the number of surplus electrons, n on each sphere, we divide q by e the electron charge.

So, n = q/e = 2.161 × 10⁻⁷ C ÷ 1.602 × 10⁻¹⁹ C = 0.6825 × 10¹² = 1.349 × 10¹² electrons

depends on what you mean by "group." for order, it would be coleoptera (beetles). for class, it would be insecta (insects). for phylum, it would be the arthropoda (animals with jointed exoskeletons).

explanation:

hypothesising or postulating