现有“6V 3W”的灯泡L₁和“6V 6W”的灯泡L₂，将他们接入电路中，不考虑灯丝电阻的变化，下列关于两只灯泡的说法正确的是（　　）

为了锻炼身体，小明利用所学物理知识设计了一个电子拉力计，图甲是原理图．硬质弹簧右端和金属滑片P固定在一起（弹簧的电阻不计，P与R₁间的摩擦不计）．定值电阻R₀=10Ω，a、b是一根长为5cm的均匀电阻丝，阻值R₁=50Ω，电源电压U=6V，电流表的量程为0～0.6A．

用括号里所给动词的适当形式填空。
(1)He often ____ (study) with his friends in the library after class.
(2)We should do more exercise ____  (keep) healthy.
(3)These magazines must not ____  (take) out of the reading room.
(4)  I called you this morning, but nobody answered it.
     Oh, we ____ (run) in the park.
(5)Jacky Chen ____  (star) in many action films for many years. I admire him very much.

质量m=1kg的物体，在水平拉力F的作用下，沿粗糙水平面运动，经过位移4m时，拉力F停止作用，运动到位移是8m时物体停止．运动过程中E_k﹣x的图线如图所示．求：