在光滑水平面上有一静止小滑块,若给滑块加一水平向右的力F1,持续一段时间后立即换成与力F1相反方向的力F2,当F2持续时间为F1持续时间的一半时撤去力F2,此时滑块恰好回到初始位置,且具有大小为p的动量.在上述过程中,F1对滑块做功为W1,冲量大小为I1;F2对滑块做功为W2,冲量大小为I2.则( )
A．I1=p/3,I2=2p/3
B．I1=p/3,I2=4p/3
C．W1=W2/8
D．W1=8W2/9
BC
设F1撤去时,滑块速度为v1,F2作用时间为t,撤去力F2时滑块速度大小为v2.由平均速度与位移的关系可得
联立解得v2=3v1.则F1对滑块的冲量大小I1=mv1=mv2/3=p/3,F2对滑块的冲量大小I2=mv2+mv1=4mv1=4mv2/3=4p/3,A错误,B正确;F1对滑块做功
F2对滑块做功
,C正确D错误.
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