As shown in the figure, a long board with a mass of M = 3kg is parked on a smooth horizontal plane, and a small block with a mass of M = 1kg is placed on the board. At a certain moment, after the two blocks and the board simultaneously obtain the initial velocity of V = 4m / S in the opposite direction, they begin to move in the opposite direction. It is known that there is friction between the boards, (1) the speed and direction of the final board and block; (2) when the board moves to the right at the speed of 2.4m/s, the speed and direction of the block

As shown in the figure, a long board with a mass of M = 3kg is parked on a smooth horizontal plane, and a small block with a mass of M = 1kg is placed on the board. At a certain moment, after the two blocks and the board simultaneously obtain the initial velocity of V = 4m / S in the opposite direction, they begin to move in the opposite direction. It is known that there is friction between the boards, (1) the speed and direction of the final board and block; (2) when the board moves to the right at the speed of 2.4m/s, the speed and direction of the block

(1) According to the law of conservation of momentum, mv1-mv1 = (M + m) v v = 2m / s. The velocity 2m / s and direction of the final board and block are the same as that of the board. (2) when the board moves to the right at the speed of 2.4m/s, the velocity and direction of the block are mv1-mv1 = M