Under the action of the horizontal constant force F, the object with mass m on the horizontal plane starts to make a uniformly accelerated linear motion from the static state, and the external force is removed after time t, and then the object moves after time 3T When the body stops, what is the resistance?

Under the action of the horizontal constant force F, the object with mass m on the horizontal plane starts to make a uniformly accelerated linear motion from the static state, and the external force is removed after time t, and then the object moves after time 3T When the body stops, what is the resistance?

Suppose the resistance is f, the acceleration during acceleration is (f-f) / m, and the acceleration during deceleration is f / m
The speed increment of accelerating motion is equal to the speed reduction of decelerating motion
t×(F-f)/m=3t×f/m
The solution is f = f / 4