1、(2009年全国卷Ⅰ)19．天文学家新发现了太阳系外的一颗行星。这颗行星的体积是地球的4.7倍，质量是地球的25倍，已知某一近地卫星绕地球运动的周期约为1.4小时，引力常量G=6.67×10^-11N·m²/kg²，由此佑算该行星的平均密度约为

A．1.8×10³kg/m³　　 B．5.6×10³kg/m³　　 C．1.1×10⁴kg/m³　　 D．2.9×10⁴kg/m³

答案D

[解析]本题考查天体运动的知识.首先根据近地卫星饶地球运动的向心力由万有引力提供,可求出地球的质量.然后根据,可得该行星的密度约为2.9×10⁴kg/m³

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