Physics 011

Chapter 3: Kinematics in Two Dimensions; Vectors
Practice Questions

A of PQ#3

1.	If you drive west at 20 km/h for one hour, then drive east at 15 km/h for one hour, your net displacement will be The correct answer: 5 km west. See Section 3-2 in Giancoli. The west velocity is greater than the East velocity.
2.	A 200-lb force is pulling on an object, as shown. The sign of the x and y components of the force are The correct answer: x (negative), y (positive). Left is negative. See Section 3-4 in Giancoli.
3.	Three boys each pull with a 20-N force on the same object. The resultant force will be The correct answer: 20 N to the left. See Section 3-2 in Giancoli.
4.	Consider a plane flying with groundspeed Vg and airspeed Va in a wind with speed V. Which of the following relationships is true? The correct answer: Vg can have any value between Va + V and Va - V See Example 3-12 in Giancoli.
5.	Two vectors, R and S, are known: If vector S is subtracted from vector R, the vector T = R - S is The correct answer: Review Section 3-3 in Giancoli.
6.	Two vectors, R and S, are known: If vector R is subtracted from vector S, the vector T = S - R is The correct answer: Review Section 3-3 in Giancoli.
7.	Two vectors, R and S, are known: If vector S is added to the vector R, then the vector T = R + S is The correct answer:
8.	If the acceleration vector of a body is perpendicular to the velocity vector, which of the following must be true? The correct answer: The direction is changing. This will never be true if the acceleration is perpendicular to the velocity. See Section 3-5 in Giancoli.
9.	A vector of magnitude 10 has an angle with the positive x-axis (East) of 120 degrees. What are its components? The correct answer: -5 and 8.7 This would be true if the vector was in the first quadrant. Review Section 3-4 in Giancoli.
10.	A vector of magnitude 10 has an angle with the positive x-axis (East) of -60 degrees. What are its components? The correct answer: 5 and -8.7 This would be true if the vector was in the first quadrant. Review Section 3-4 in Giancoli.
11.	A vector has components x=6 m and y=8 m. What is its magnitude and direction? Your answer: 10 m and 30 degrees The correct answer: 10 m and 53 degrees Your magnitude is correct. Review Section 3-4 in Giancoli.
12.	A vector has components x= -2 m and y=-2 m. What is its direction (angle with respect to East)? The correct answer: 225 degrees This answer is in the first quadrant. Review Section 3-4 in Giancoli.
13.	Three vectors have components (x,y):A=(2,3),B=(4,-7) and C=(-6,-3). What is the magnitude of the resultant vector (D=A+B+C)? The correct answer: 7 The magnitude is always positive. Review Section 3-4 in Giancoli.
14.	Three vectors have components (x,y):A=(2,3),B=(4,-7) and C=(-6,-3). What is the magnitude of the resultant vector (D=A-B-C)? The correct answer: 13.6
15.	Suppose that several projectiles are fired on level ground. Which one will be in the air longest? The correct answer: The one with the highest maximum elevation, h. Review example 3-4 in Giancoli.
16.	Which of the following does not affect the range of a projectile? The correct answer: xo Initial Horizontal Position Review Example 3-8 in Giancoli.
17.	Which of the following must be zero for a projectile to achieve its maximum range? The correct answer: yf If this were true the projectile would not have moved at all. See Example 3-7 in Giancoli.
18.	Which of the following must be zero for a projectile to be at its maximum height? The correct answer: vyf Its elevation is independent of its horizontal motion. See Example 3-4 in Giancoli.
19.	You hit a handball too hard and it lands, moving horizontally, on top of a roof. If its original velocity was vo at an angle q above the horizontal, then the velocity it lands on the roof with is The correct answer: vo cos q Good try, but still wrong. Projectile motion ends just before the projectile hits the ground. See Example 3-4 in Giancoli.
20.	You throw a pebble upward as shown, with a velocity vo at an angle theta, from a roof (at point J) h ft above the ground. If the pebble rises upward to h ft above the roof (to point K), then falls to the ground below (to point L), its speed when it hits the ground is The correct answer: between vo and 2vo. This is the maximum speed it would have upon passing the roof on the way down. Review Section 3-6 in Giancoli.
21.	Taking "up" as positive at the highest point, the acceleration of a projectile is
22.	If the sum of two vectors equals zero, the magnitude of their difference is The correct answer: equal to twice the magnitude of either one.
23.	A sailboat travelling with a speed of 4 knots heads directly up river against a 3 knot current. Its speed over ground is The correct answer: 1 knot. The boat speed is measured with respect to the water and the water is moving over the ground. Review Section 3-8 in Giancoli.
24.	A sailboat travelling with a speed of 4 knots heads directly down river with a 3 knot current. Its speed over ground is The correct answer: 7 knots. Remember that they are in the same direction. Review Section 3-8 in Giancoli.
25.	A sailboat travelling with a speed of 4 knots heads directly across a river which has a 3 knot current. Its speed over ground is The correct answer: 5 knots.