1. The problem statement, all variables and given/known data A ball is thrown vertically upward with an initial speed of v0. It experiences a force of air resistance. The positive direction for all vector quantities is upward. Does the magnitude of the acceleration of the ball increase, decrease, or remain the same as the ball moves upwards? 3. The attempt at a solution The magnitude of the ball’s acceleration with air resistance increases as the ball moves upwards because air resistance acts downwards, and the acceleration due to gravity also acts downwards. Acceleration becomes more negative, increasing the magnitude of the acceleration. For example, if the acceleration due to gravity is -9.80m/s2 and the acceleration due to air resistance is -1.00m/s2, then: Acceleration without air resistance = -9.80m/s2 Acceleration with air resistance = -9.80m/s2 + (-1.00m/s2) = -10.8m/s2 Comparing only the magnitudes of the accelerations: Magnitude of acceleration without air resistance = 9.80m/s2 Magnitude of acceleration with air resistance = 10.8m/s2 The magnitude of the acceleration with air resistance is greater than the magnitude of the acceleration without air resistance. However, the AP exam (question 1a) has the same question and this is their answer: Question: http://apcentral.collegeboard.com/apc/public/repository/_ap05_frq_physics_c_m_45648.pdf Solution: http://apcentral.collegeboard.com/apc/public/repository/_ap05_sg_physics_c_me_46691.pdf Since velocity is upward, air resistance is downward, in the same direction as gravity. The velocity will decrease, causing the force of air resistance to decrease. Therefore, the net force and thus the total acceleration both decrease. Which answer is right? Did the AP solution maybe forget that the question asked for magnitude?