如圖所示,彈簧秤外殼質(zhì)量為m,彈簧及掛鉤的質(zhì)量忽略不計(jì),掛鉤上吊一重物.現(xiàn)用一豎直向上的外力拉彈簧秤,當(dāng)彈簧秤向上做勻速直線運(yùn)動時,示數(shù)為F
1;若讓彈簧秤以加速度a向上做勻加速直線運(yùn)動,則彈簧秤的示數(shù)為(重力加速度為g)( ?。?br/>
![](http://hiphotos.baidu.com/zhidao/pic/item/fcfaaf51f3deb48fa35bf469f31f3a292df57852.jpg)
A. mg
B. F
1+mg
C. F
1+ma
D. (1+
)F
1
設(shè)物體的質(zhì)量為m
0,當(dāng)彈簧秤向上做勻速直線運(yùn)動時,示數(shù)為F
1,F(xiàn)
1=m
0g.
當(dāng)彈簧秤以加速度a向上做勻加速直線運(yùn)動,根據(jù)牛頓第二定律得,F(xiàn)
2-m
0g=m
0a,解得
F2=(1+)F1.故D正確,A、B、C錯誤.
故選D.