表示
大炮炮身的质量是1t,它水平发射一颗质量为2.5kg的炮弹,炮弹飞出炮口时的速度是600m/s,则炮身后退的速度是____m/s.
大炮炮身的质量是1t,它水平发射一颗质量为2.5kg的炮弹,炮弹飞出炮口时的速度是600m/s,则炮身后退的速度是\_\_\_\_m/s.
Young boys and girls stood on _____ sides of the street to welcome the president from Africa.
Young boys and girls stood on \_\_\_\__ sides of the street to welcome the president from Africa.