A 2kg textbook rests on a frictionless, horizontal surface. A cord attached to the book passes over a pulley whose diameter is 0.15m, to a hanging book with mass 3kg. The system is released from rest, and the books are observed to move 1.2m in 0.8s.

My solution so far:

using constant acceleration formula

For the hanging part:

(rounded) This agrees with my textbook

however for the horizontal tension in the cord

I make it

however the answer in my textbook is 7.5 which would suggest

where has the force gone?

Have I missed out a force

Also how can you have different tensions in the cord surely it would snap?