Lightly spoon flour into a dry measuring cup; level with a knife. Combine flour, rhubarb, and sugar; toss well. Let stand 20 minutes, stirring occasionally.
Preheat oven to 350°.
Roll dough into an 11-inch circle. Fit dough into a 10-inch round removable-bottom tart pan. Press dough against bottom and sides of pan, and place in the freezer for 10 minutes. Spoon the rhubarb mixture into crust. Bake at 350° for 55 minutes. Cool completely, and cut into wedges. Serve with whipped topping.