一质点在外力作用下运动时 下列说法哪个正确？ Which of the following statements is true when
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一质点在外力作用下运动时，下列说法哪个正确？ Which of the following statements is true when a particle moves under the action of an external force？
A．质点的动量改变时，质点的动能也一定改变； When the momentum of the particle changes, the kinetic energy of the particle also changes;
B．质点的动能不变时，质点的动量也一定不变； When the kinetic energy of the particle is constant, the momentum of the particle is also constant;
C．外力的功是零，外力的冲量一定是零； The work of external force is zero, and the impulse of external force must be zero;
D．外力的冲量是零，外力的功也一定是零； The impulse of the external force is zero, and the work of the
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D