A:温度升高,内能增加600J
B:温度升高,内能减少200J
C:温度降低,内能增加600J
D:温度降低,内能减少200J
回答问题(简答)。
Lucy is my good friend. She is eleven years old. She is a student. She likes singing. She has a nail pet. Her name is Kitty. Look, Lucy's singing and the cat is dancing. Lucy wants to be a singer when she grows up.
Lucy's mother is a nurse. She works in a hospital. She likes shopping. She usually buys a lot of beautiful clothes at weekends.
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弹簧受力时一般遵循“胡克定律”,即:在一定的范围内,弹簧所受拉力F的大小跟弹簧伸长量x成正比,即F=kx,式中k称为弹簧的“劲度系数”,单位是“N/m”.已知:某弹簧不受任何力时长度为12cm,当该弹簧受到拉力F1=2N时长度为16cm;受到拉力F2时长度为18cm.已知:拉力F1、F2均在该弹簧一定的范围内,求该弹簧的劲度系数k和拉力F2的大小.