Question

You have a lightweight spring whose unstretched length is 4.0 cm. First, you attach one end of the spring to the ceiling and hang a 3.0 g mass from it. This stretches the spring to a length of 5.0 cm . You then attach two small plastic beads to the opposite ends of the spring, lay the spring on a frictionless table, and give each plastic bead the same charge. This stretches the spring to a length of 4.6 cm .

What is the magnitude of the charge (in nC) on each bead?

Express your answer using two significant figures.

Answer 1

Solution : unstretched length of spring (L) = 4 cm = 4x16² m mass attached to the spring (m) = 39 = 3x10 kg stretch in spring length x = (5-4) x102 ma ooolm. Total Stretch in spring when beads are attached n = 4otx 10²m. = 0.046 m Now from Hook's low akn & mg = 3x10 3 x 9.8 = 2.94N/m 0.01 F- let the charse Fe = on each bead is al F & 4x 109 x 2 Hook's low 4 147.36 x 10-18 -2.940.006 Electric 2 - az = up (4.6x10272 97036 x 64.4x109 c is effective stretch length after charge uplacta - 90 - =) = 6404 nc/