University Physics Al No. 3 Newton's Laws of motion Class Number ame I. Choose the Correct Answer 1. Which statement is most correct? (C) (A)Uniform circular motion causes a constant force toward the center B)Uniform circular motion is caused by a constant force toward the center (C)Uniform circular motion is caused by a constant magnitude net force toward the center (D)Uniform circular motion is caused by a constant magnitude net force away the cent Solution: For uniform circular motion, the speed or the angula d of the particle is a constant According to F =ma= m-=mo r, the magnitude of the force toward the center should be constant 2. Suppose the net force F on an object is a nonzero constant Which of the following could also (A)Position. (B)Speed. ( C) Velocity. (D) Acceleration Solution: According to Newton's second law F=ma, the answer is(D) 3. Which of the graph in Figure 1 best shows the velocity-time graph for an object launched vertically into the air when air resistance is given by D=br? The dashed line shows the velocity graph if there was no air resistance Solution: During the course of the object moves up, the acceleration of the object thinking about air resistance is more than that no air resistance, that is that the tangent of the graph should be more than that no air resistance. Thus we remove the answer(D) During the course of the object moves down, when t->00, a>0,v>constant. Thinking about this, the right answer is(B) I Filling the blankUniversity Physics AI No. 3 Newton’s Laws of Motion Class Number Name I．Choose the Correct Answer 1. Which statement is most correct? ( C ) (A) Uniform circular motion causes a constant force toward the center. (B) Uniform circular motion is caused by a constant force toward the center. (C) Uniform circular motion is caused by a constant magnitude net force toward the center. (D) Uniform circular motion is caused by a constant magnitude net force away the center. Solution: For uniform circular motion, the speed or the angular speed of the particle is a constant. According to m r r v Fc mac m 2 2 = = = ω , the magnitude of the force toward the center should be constant. 2. Suppose the net force F r on an object is a nonzero constant. Which of the following could also be constant? ( D ) (A) Position. (B) Speed. (C) Velocity. (D) Acceleration. Solution: According to Newton’s second law F ma r r = , the answer is (D). 3. Which of the graph in Figure 1 best shows the velocity-time graph for an object launched vertically into the air when air resistance is given by D=bv? The dashed line shows the velocity graph if there was no air resistance. ( B ) Solution: During the course of the object moves up, the acceleration of the object thinking about air resistance is more than that no air resistance, that is that the tangent of the graph should be more than that no air resistance. Thus we remove the answer (D). During the course of the object moves down, when t → ∞ , a → 0 , v → constant . Thinking about this, the right answer is (B) II. Filling the Blanks t v t v t v t v (A) (B) (C) (D)