(2) The magnitude of the ampere force on the rod is fa = bil = bblvr+rl = b2l2vr+r+R..
For the rod, according to Newton's second law, F+mgsinθ-FA=ma,
Substituting F=0.5v+2 gives: 2+mgsinθ+(0.5-B2L2R+r)v=ma,
Because the acceleration a of uniform acceleration motion has nothing to do with v,
So a=2+mgsinθm=8m/s2,
0.5-B2L2R+r=0,
R = 0.3 ω。
(3) From x= 12at2, the required time is t=2xa=2× 18s=0.5s, and the speed of ab rod is v=at=4m/s?
The total joule heat in the circuit is q = r+rrq1= 0.3+0.20.3× 0.8j = 43j.
According to the law of conservation of energy, W+mgxsinθ=Q+ 12mv2.
Solution: w =103j ≈ 3.3j.
Answer: (1) The metal bar accelerates uniformly.
(2) The resistance value of resistor R is 0.3 Ω.
(3) The time t required for this process is 0.5s, and the work w done by pulling force F is 3.3J 。