小明同学用如图甲所示的装置进行“探究加速度与力、质量的关系”的实验.
一个可视为质点的小球被长为L的绳悬挂于O点,空气阻力忽略不计,开始时绳与竖直方向的夹角为α,在球从A点由静止开始运动到等高点C点的过程中(B点是运动过程中的最低点),下列说法正确的是( )
Lincheng is a new developing city. There are lots of popular restaurants. Although they are not famous, they are good places to have meals.
Qingteng Yuan
Main dishes: Many different fish, meat and chicken dishes
Specials: Vegetable salad (¥20),
Roast beef (¥48 on weekdays, ¥38 on weekends)
Fruits (Free): Watermelon, apples, bananas, oranges
Tel: 876-2198
Opening Hours: 11:00 a.m.—1:00 a.m.
Ruihai Drinking
Building
Mainly all kinds of meat, pork, beef and mutton.
Specials: Roast pork (only offered on Saturday, ¥50 each)
Drinks are not allowed to take except VIP.
Tel: 897-6543
Opening Hours: 11:00 a.m.—1:30 a.m. (VIP 24 hours)
Rujia Restaurant
Mainly dumplings and noodles.
Specials: Beef and cabbage dumplings (¥5 each on weekdays, ¥4.5 on weekends)
Dumplings can be taken away.
Tel: 432-0945
Opening Hours: 11:30 a.m.—10:00 p.m.
Linglong Sea Food
Mainly sea food.
Specials: Roast fish (¥25 each)
Tel: 287-9056
Opening Hours: 11:00 a.m.—12:00 p.m. (From Monday to Thursday)
11:00 a.m.—2:00 a.m. (Friday, Saturday, Sunday)
如图所示的电路,R2=2R1,电源电压保持不变,当开关S由断开变为闭合时,电流表的示数( )