A plastic sphere carrying a charge of is fired directly toward a stationary point…
PHYSICS · Multi-part · A Level · Physics · Fields and their consequences · Fields and their consequences
Problem
A 5.0×10−3kg plastic sphere carrying a charge of +2.0μC is fired directly toward a stationary point charge of +8.0μC. The initial separation between the centers of the two charges is 1.50m, and the sphere’s initial speed is 60m/s.
Ignore all forces except those between the two charges. The stationary charge is sufficiently massive that its motion may be neglected.
Constant: k=8.99×109N⋅m2/C2.
(a) Derive an expression relating the sphere’s speed v to its distance r from the stationary charge, using appropriate conservation principles.
(b) Determine the distance of closest approach between the two charges.
(c) Calculate the sphere’s speed when the separation is 0.50m and state whether the sphere is moving toward or away from the stationary charge at that instant.
(d) Suppose the initial speed were doubled while all other parameters remained the same. Without performing a full recalculation, describe qualitatively how the distance of closest approach would change and provide a brief justification.