质量为m的运动质点,受到某力的冲量后,速度v的大小不变,而方向改变了角,则这个力的冲量的大小为 [ ] A. <br/> <img src="https://static.zxtiku.com/wangke/imgs/topic/f7c7a1a2242db91c4d46f49547765fed.jpg"/>; B. <br/> <img src="https://static.zxtiku.com/wangke/imgs/topic/2d1540282abfd9488b33fa177200033c.jpg"/>; C. <br/> <img src="https://static.zxtiku.com/wangke/imgs/topic/f402c828d62dff24e1132fdcbd0e326e.jpg"/>; D. <br/> <img src="https://static.zxtiku.com/wangke/imgs/topic/5b8264df5a565ceb37481ab135dcc367.jpg"/>。