19) Jan and Len throw identical rocks off a tall building at the same time. The ground near the building is flat. Jan throws her rock straight downward. Len throws his rock downward and outward such that the angle between the initial velocity of the rock and the horizon is 30. Len throws the rock with a speed twice that of Jan's rock. If air resistance is negligible, which rock hits the ground first? A) They hit at the same time. B) Jan's rock hits first. C) Len's rock hits first. D) It is impossible to know from the information given. 20) For general projectile motion, when the projectile is at the highest point of its trajectory; A) its acceleration is zero. B) its velocity is perpendicular to the acceleration. C) its velocity and acceleration are both zero. D) the horizontal component of its velocity is zero. E) the horizontal and vertical components of its velocity are zero. 21) An electron moves with a constant horizontal velocity of 3.0 x 106 m/s and no initial vertical velocity as it enters a deflector inside a TV tube. The electron strikes the screen after traveling 17.0 cm horizontally and 40.0 cm vertically upward with no horizontal acceleration. What is the constant vertical acceleration provided by the deflector? (The effects of gravity can be ignored.) A) 2.5 x 10* m/s- B) 8.3 x 10- m/s- C) 1.4 x 10# m/s- D) 1.2 * 1014 m/62