PHYS1230: General Physics Problems Name: Date Practice 4: Applying Newtown's Laws 1. A block with a mass of 1 kg is placed on a vertical wall -- see figure below. The coefficient of static friction is 0.6. With what magnitude force do you need to push on the block perpendicular to the wall to keep the block from falling? 1 kg F 2. Similar to part 1), but now you push the block with a constant force F at a certain angle 0=450 with respect to the horizontal line - see figure below, so that the block moves upward along the wall with a constant acceleration a=2.2 m/s'. Find the magnitude of force F if the coefficient of kinetic friction is 0.5. 1 kgPHY51230: General Physics Problems Name: Date Practice 6: Work 8'. Kinetic Energy Problem 1. A box of mass m=1 kg is sliding with a constant speed of 4.5 m/s on a frictionless horizontal surface when, at point P, it encounters a rough section. The coefficient of kinetic friction in the rough section is not constant; it starts at 0.1 at P and increases linearly with distance past P, reaching a value of 0.6 at 12.5 m past point P. How far from point P does this box slide before stopping? 'Uz' '- (m '////////////////////////////1 P Mela?) Conceptual analysis: We want to calculate the work done by friction and apply work-energy theorem. Since the friction is not constant, we have to use the general expression to calculate the work. P2_, _. W2] F-dl P1 1. Use the problem statement to write an expression for pk. Which expression is correct? Here A represents a number. A) MKCX): 0.6 + Ax B) ux) = 4.5 + Ax C) ux) = 0.1 + Ax 2. What is the value ofA. m use initial conditions to find the value. A) A = 0.04 m'l B) A = 25 m-' C) A = 0.048 m4 D) A = 1.25 m'1 PHYS1230: General Physics Problems 3. Now calculate the work done by the friction force Wext = AK to find the distance d that the box travels in the rough surface before stopping. Hint: Use fk = MK mg along with the correct expression for /k. N