题目内容


从地面上方某点,将一小球以2m/s的初速度沿水平方向抛出,到落地时运动的水平距离为x=1.6m,不计空气阻力,取g=10m/s2.求:                                                                                                           

(1)小球在空中运动的时间;                                                                                    

(2)小球抛出点的高度.                                                                                           

                                                                                                                                   


(1)小球在空中的运动时间为:t=

(2)小球抛出点的高度为:h=

答:(1)小球在空中运动的时间为0.8s;

(2)小球抛出点的高度为3.2m.


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如图所示,一个质量为m=4kg的物体,受到与水平方向成37角斜向下方的推力F1=20N的作用,在水平地面上移动了距离l1=2m后撤去推力,此后物体又滑行了l2=1.4m,的距离后停止了运动.设物体与地面间的滑动摩擦力为它们间弹力的0.2倍(sin37°=0.6                                                                    cos37°=0.8 g=10m/s2),求:                

(1)推力F1对物体做的功;                                                                                      

(2)全过程中摩擦力对物体所做的功;                                                                     

(3)推力作用时合外力对物体所做的总功.                                                              

                                                                                              

                                                                                                                                   

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