a A = 15-5 4 m/ s 2 =2.5m/ s 2。

Speed: v A = 5m/s

According to Newton's second law, the acceleration after movement is: a= mgsinθ-μmgcosθ-kv m …①.

When the acceleration a=0, the speed reaches the maximum value, v m =10 m/s.

There are: MGS in θ-μ m GC OS θ-KVM = 0 ... ②.

Simultaneous ① ② solution: μ= 1 8, k = 20N/M. S- 1.

Because this motion is an accelerated motion with varying acceleration, it is impossible to find out the time required for the sled to reach the maximum speed. So a, b and c are right and d is wrong.

This question is uncertain, so choose D.