mechanics

When a particle is acted on by a constant force, which of the following will change with time?

(1) the acceleration of the particle
(2) the momentum of the particle
(3) the kinetic energy of the particle

Assume the constant force is given to the moving direction and that direction are taken as positive.

1) False
By F=ma
when constant force are given, it will also have CONSTANT acceleration as mass is unchanged.

2) True
By momentum = mv
The velocity increase by time to time as there are acceleration
Mass is unchanged.
Hence the momentum is increase by time to time

3) True
By KE = 0.5 * m * v^2
The velocity increase by time to time as there are acceleration
Mass is unchanged and 0.5 is a constant
KE increase by time to time

原因十分之簡單,你想一想當你拋一件東西垂直地向天時,有一個固定的力會拉住它的,這力叫萬有引力是向下的,這個力是固定而不變的(9.8ms-2),如果拋的高度不是十分高的.所以(1)錯.動量等如m乘v,因為當向上拋時,物體的速度會減小,即表示它的動量也會隨時間而變化,所以(2)是正確的.由於速度會減小,所以動能也會減小的,所以(3)正確
希望幫到你.

same net force same acceleration

2007-05-01 01:54:37 補充：
since acceleration exists,v increase so momentum n ke also increase