If work is done by a body against a force,is the work considered positive or negative?

$A$ ball of mass $m$ is attached to a string whose other end is fixed. The system is free to rotate in a vertical plane. When the ball swings,no work is done on the ball by the tension in the string. Which of the following statements is the correct explanation?

$A$ cyclist comes to a skidding stop in $10 \,m$. During this process,the force on the cycle due to the road is $200 \,N$ and is directly opposite to the motion. How much work does the road do on the cycle?

When a body moves in a circular path,no work is done by the centripetal force since

$A$ block of mass $m$,kept on a horizontal surface,is moved through a distance $s$ by applying a horizontal force $F$ to it. What is the work done by the normal reaction?

Given that $W = \vec F \cdot \vec s = 0$ and $F \neq 0, s \neq 0$,then