[填空题]
Two blocks of masses $3.0\,kg$ and $4.0\,kg$ are held stationary with a thread connecting the blocks. The mass of $43.0\,kg$ is on a rough incline that makes an angle of $30^{\circ}$ with the ground and it starts to slip up when the other mass is slightly more than $4.0\,kg$.
1.State two differences between static friction and dynamic friction
2.Calculate the coefficient of static friction between the mass of $3.0\,kg$ $N$ and the rough surface.
3.The thread connecting masses breaks and the mass of $3.0\,kg$ slides down. The acceleration of the mass of $3.0\,kg$ is around $m\;s^{-2}$. The coefficient of dynamic friction between $3.0\,kg$ mass and the rough surface is 0.40.
4.The speed of the mass of $3.0\,kg$ after it has moved through a vertical height of $1.0\,m$. $m\;s^{-1}$
