1. A 150 Newton horizontal force pushes a 20 kg mass sitting on a horizontal surface. Additionally, the horizontal surface exerts a 50 Newton frictional force on the mass. What is the acceleration of the mass? 3. Rhenium-186 is a beta emitter with weak gamma emission useful for imaging. If a sample has an initial activity of 18.0 Ci, what is the activity 19 days later? The half-life of rhenium-186 is 3.8 days. 5. A solution has a hydronium-ion concentration of 1.0 x 10-2 mol per liter. What is the pH of this solution? Is this solution acidic or basic? What is the hydroxide-ion concentration of this solution?