3. A force is exerted on a positively-charged particle that moves the particle in the direction opposite to that of an electric
field. Which one of the following statements concerning the work performed in this movement is true? a) The work done on the particle has a positive sign. b) No work is done on such a charged particle, if it is moved in a direction that is parallel or anti-parallel to an electric field. c) The work done on the particle has a negative sign. d) One cannot answer this question without knowing the kind of particle involved
a) The work done on the particle has a positive sign.
Explanation:
When a positive charge is placed in a electric field , a force is exerted by electric field along the direction of the electric field . But the external force is acting on it so that displacement is opposite to the field . That means the external force is acting opposite to electric force on the charged particle.
The displacement is along the external force applied so both force and displacement are positive . Hence work done is positive .
Work done by electric field is negative , because displacement and electric force are opposite.
Impulse = Change in momentum. The ball was moving with a momentum of 0.45 * 22 = 9.9 The ball comes to rest in the receivers arm; this means the ball's final velocity = 0. So mv2 = 0.45 * 0 The magnitude of the impact is just the change in momentum. 9.9 - (0.45 * 0) = 9.9
