问题
单项选择题
When should distress flares and rockets be used? （）
A.Immediately upon abandoning the vessel
B.Only when there is a chance of their being seen by a rescue vessel
C.At one hour intervals
D.At half hour intervals
答案
参考答案：B
。物块A、B质量mA=mB=1kg。开始时A、B静止，A、B间压缩一轻质弹簧，贮有弹性势能Ep=16J。现解除锁定，弹开A、B，弹开后弹簧掉落，对A、B此后的运动没有影响。g=10m/s2。求： 