University Physics Al No. 2 Motion in two and Three dimensions Class Number ame I. Choose the correct answer An object moves in the xy plane with an acceleration that has a positive x component. At time t=0 the object has a velocity given by v=3i+0j. What can be concluded about the y component of the acceleration? (A)The y component must be positive and constant. B) The y component must be negative and constant (C)The y component must be zero (D) Nothing at all can be concluded about the y component dt Solution: According to the general equations a we just know the initial velocity of the object, so nothing at all can be concluded about the y component 2. An object moves with a constant acceleration a. Which of the following expression are also ( B d(v2) / (B) Solution: According to the general equation a=-, we know the velocity v is vary with time So the magnitude and the direction of the velocity may not constant so(A),(C)and(D)are not corrected.As a=h=constant, Answer(B)is the right answer dt 3. An object is launched into the air with an initial velocity given by vo=(4.9i+9.8])m/s Ignore air resistance. At the highest point the magnitude of the velocity (B) (A)0.(B)√495ms.(C)√98ms.(D)√(49)2+(98)ms Solution: The y component of the velocity is zero at the highest point, and the x component of the velocity is 4.9m/s, thus the velocity is v=(4.9i)m/s, the magnitude is 4.9m/sUniversity Physics AI No. 2 Motion in Two and Three Dimensions Class Number Name I．Choose the Correct Answer 1. An object moves in the xy plane with an acceleration that has a positive x component. At time t = 0 the object has a velocity given by v i j = 3ˆ + 0 ˆ r . What can be concluded about the y component of the acceleration? ( D ) (A) The y component must be positive and constant. (B) The y component must be negative and constant. (C) The y component must be zero. (D) Nothing at all can be concluded about the y component. Solution: According to the general equations t v a x x d d = and t v a y y d d = , we just know the initial velocity of the object, so nothing at all can be concluded about the y component. 2. An object moves with a constant acceleration a r . Which of the following expression are also constant? ( B ) (A) t v d d r . (B) t v d d r . (C) t v d d( ) 2 . (D) t v v d d( / ) r r . Solution: According to the general equation t v a d d v v = , we know the velocity v v is vary with time. So the magnitude and the direction of the velocity may not constant. so (A), (C) and (D) are not corrected. As constant d d = = t v a v v , Answer (B) is the right answer.. 3. An object is launched into the air with an initial velocity given by )m/s 8 ˆ 9. 9ˆ (4. 0 v = i + j r . Ignore air resistance. At the highest point the magnitude of the velocity is ( B ) (A) 0. (B) 4.9 m/s 2 . (C) 9.8 m/s 2 . (D) (4.9) (9.8) m/s 2 2 + . Solution: The y component of the velocity is zero at the highest point, and the x component of the velocity is 4.9m/s, thus the velocity is )m/s 9ˆ v = (4. i r , the magnitude is 4.9m/s