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英语物理题1题.A boy is pushing,horizontally,a box of old newspaper

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英语物理题1题.
A boy is pushing,horizontally,a box of old newspapers of mass 8kg along a straight path,against a frictional force of 16N.Calculate the force with which the boy is pushing when he is moving.
(a)with constant speed
(b)with a constant acceleration of 1.2ms^-2
英语物理题1题.A boy is pushing,horizontally,a box of old newspaper
一男孩在水平方向上沿直线推一个装了旧报纸的盒子,它重8kg,受到摩擦力16N,计算男孩的推力.
(1)在匀速下
(2)在匀加速下,加速度为1.2
(1)匀速下,受力平衡,推力等于摩擦力,为16N
(2)匀加速下,合力产生加速度,由牛顿第二定律得:F-f=ma,F是推力,f是摩擦力,可得,F=25.6N