1.
Incorrect 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
Your Answer:
5 km east.
Correct Answer:
5 km west.
Review Chapter 3 in Giancoli. The west velocity is greater than the east velocity.
2.
Incorrect
A 200-lb force is pulling on an object, as shown. The sign of the x and y components of the force are
Your Answer:
x (positive), y (positive).
Correct Answer:
x (negative), y (positive).
Left is negative. Review Chapter 3 in Giancoli.
3.
Incorrect
Three boys each pull with a 20-N force on the same object. The resultant force will be
Your Answer:
zero.
Correct Answer:
20 N to the left.
Review Chapter 3 in Giancoli.
4.
Incorrect Consider a plane flying with groundspeed Vg and airspeed Va in a wind with speed V. Which of the following relationships is true?
Your Answer:
Vg will always equal Va + V
Correct Answer:
Vg can have any value between Va + V and Va - V
Review the Examples in Chapter 3 in Giancoli.
5.
Incorrect Two vectors, R and S, are known:
If vector S is subtracted from vector R, the vector T = R - S is
Your Answer:
Correct Answer:
Review Chapter 3 in Giancoli.
6.
Incorrect Two vectors, R and S, are known:
If vector R is subtracted from vector S, the vector T = S - R is
Your Answer:
Correct Answer:
Review Chapter 3 in Giancoli.
7.
Correct Two vectors, R and S, are known:
If vector S is added to the vector R, then the vector T = R + S is
Your Answer:
8.
Incorrect If the acceleration vector of a body is perpendicular to the velocity vector, which of the following must be true?
Your Answer:
The speed is changing.
Correct Answer:
The direction is changing.
This will never be true if the acceleration is perpendicular to the velocity. Review Chapter 3 in Giancoli.
9.
Incorrect A vector of magnitude 10 has an angle with the positive x-axis (east) of 120 degrees. What are its components?
Your Answer:
5 and 8.7
Correct Answer:
-5 and 8.7
This would be true if the vector was in the first quadrant. Review Chapter 3 in Giancoli.
10.
Incorrect A vector of magnitude 10 has an angle with the positive x-axis (east) of -60 degrees. What are its components?
Your Answer:
5 and 8.7
Correct Answer:
5 and -8.7
This would be true if the vector was in the first quadrant. Review Chapter 3 in Giancoli.
11.
Incorrect A vector has components x = 6 m and y = 8 m. What is its magnitude and direction?
Your Answer:
10 m and 30 degrees
Correct Answer:
10 m and 53 degrees
Your magnitude is correct. Review Chapter 3 in Giancoli.
12.
Incorrect A vector has components x = -2 m and y = -2 m. What is its direction (angle with respect to east)?
Your Answer:
45 degrees
Correct Answer:
225 degrees
This answer is in the first quadrant. Review Chapter 3 in Giancoli.
13.
Incorrect 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)?
Your Answer:
-7
Correct Answer:
7
The magnitude is always positive. Review Chapter 3 in Giancoli.
14.
Correct 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)?
Your Answer:
13.6
15.
Incorrect Suppose that several projectiles are fired on level ground. Which one will be in the air longest?
Your Answer:
The one with the farthest range, R.
Correct Answer:
The one with the highest maximum elevation, h.
Review the Examples in Chapter 3 in Giancoli.
16.
Incorrect Which of the following does not affect the range of a projectile?
Your Answer:
V0 Initial Speed
Correct Answer:
x0 Initial Horizontal Position
Review the Examples in Chapter 3 in Giancoli.
17.
Incorrect Which of the following must be zero for a projectile to achieve its maximum range?
Your Answer:
Vxf
Correct Answer:
yf
This is an easy mistake to make. The range is achieved just before the projectile hits the ground. Review the Examples in Chapter 3 in Giancoli.
18.
Incorrect Which of the following must be zero for a projectile to be at its maximum height?
Your Answer:
Vxf
Correct Answer:
Vyf
Its elevation is independent of its horizontal motion. Review the Examples in Chapter 3 in Giancoli.
19.
Incorrect You hit a handball too hard and it lands, moving horizontally, on top of a roof. If its original velocity was V0 at an angle θ above the horizontal, then the velocity it lands on the roof with is
Your Answer:
zero
Correct Answer:
V0cos θ
Good try, but still wrong. Projectile motion ends just before the projectile hits the ground. Review the Examples in Chapter 3 in Giancoli.
20.
Incorrect You throw a pebble upward as shown, with a velocity V0 at an angle θ, 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
Your Answer:
V0.
Correct Answer:
between V0 and 2V0.
This is the maximum speed it would have upon passing the roof on the way down. Review Chapter 3 in Giancoli.
21.
Correct Taking "up" as positive at the highest point, the acceleration of a projectile is
Your Answer:
-9.8 m/s2
22.
Incorrect If the sum of two vectors equals zero, the magnitude of their difference is
Your Answer:
equal to the magnitude of either one.
Correct Answer:
equal to twice the magnitude of either one.
The sum is zero. Review Chapter 3 in Giancoli.
23.
Correct A sailboat travelling with a speed of 4 knots heads directly up river against a 3 knot current. Its speed over ground is
Your Answer:
1 knot.
24.
Incorrect A sailboat travelling with a speed of 4 knots heads directly down river with a 3 knot current. Its speed over ground is
Your Answer:
1 knot.
Correct Answer:
7 knots.
Remember that they are in the same direction. Review Chapter 3 in Giancoli.
25.
Incorrect 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
Your Answer:
1 knot.
Correct Answer:
5 knots.
This would be true if the velocities were co-linear and opposed. Review Chapter 3 in Giancoli.