Question

A ball of mass 5g and charge 10^-7 c moves from point a whose potential is 500v to a point b whose potential is zero. What is the velocity of the ball at point a if at the point b it is 25cm per second?

Answer 1

Sol. Let u be the velocity of the ball at point A.

Workdone on the charge by the field

W = q (VA – VB)

= 10–7 (500 – 0) = 5 × 10–5 J

This appears in from of the increased K.E.

∴ W = 12 mv2 –12 mu2

5 × 10–5 = 12.51000[(14)2−u2]

2 × 10–2 =116 – u2

or u2 = 116–150=17400

u = 4.1220 = 0.206 m/s = 20.6 cm/sec.

Answer 2

Answer:

Explanation:

Let u be the velocity of the ball at point A.

Workdone on the charge by the field

W = q (VA – VB)

= 10–7 (500 – 0) = 5 × 10–5 J

This appears in from of the increased K.E.

∴ W = 12 mv2 –12 mu2

5 × 10–5 = 12.51000[(14)2−u2]

2 × 10–2 =116 – u2

or u2 = 116–150=17400

u = 4.1220 = 0.206 m/s = 20.6 cm/sec.