According to the theorem of kinetic energy, in the first period of time Δ t1,the work done by a constant force (resultant force) on an object is equal to the increase of kinetic energy of the object:

W 1=0.5mv^2-0

Δ T2, w2 = 0.5m (2v) 2-0.5mv2 =1.5mv2 > w1

According to the momentum theorem, the constant force impulse is equal to the increment of the momentum of the object, and the constant force impulse is at the first time.

I 1=mv-0, the second I2=m(2v)-mv=mv=I 1.