Momentum: when m and V are constant, only the direction of V changes, then the momentum changes

Momentum: when m and V are constant, only the direction of V changes, then the momentum changes

Note that momentum is a vector. It changes in magnitude and direction, and momentum changes as well
High school physics usually only involves size change
Changes in direction need to be classified
In the case of rotation, the angular momentum is usually calculated
If it's not rotation, use vector subtraction

The momentum direction of a moving object at any moment must be the velocity direction at that moment,

I think it's right
P=mV,
The direction of V is the direction of P

A. The mass of B is m and 2m respectively, and they move with the same momentum on a smooth horizontal plane. After the collision, the direction of motion of a remains unchanged, but the velocity is reduced to half of the original, so the ratio of the velocity of a and B is ()
A. 1：2B. 1：3C. 2：1D. 2：3

Before the collision, the momentum of a and B are equal. If the velocity of a before the collision is VA, then the velocity of B is 12va. The momentum is conserved in the collision process. The initial velocity direction of a is the positive direction, and the velocity of a after the collision is: VA = 12va ′ ① According to the law of conservation of momentum, 2MVA = m · 12va + 2mvb ′, VB ′ = 34va ② From ①: ②: VA ′: VB ′ = 2:3; therefore: D