Chapter 3 Physics

A boat, whose speed in still water is 1.75 m/s, must aim upstream at an angle of 26.3e (with respect to a line perpendicular to the shore) in order to travel directly across the stream. (a) Determine the speed of the current. (b) Determine the resultant speed of the boat with respect to the shore.

(a) 0.775 m/s (b) 1.57 m/s

A projectile is shot horizontally at 23.4 m/s from the roof of a building 55.0 m tall. (a) Determine the time necessary for the projectile to reach the ground below. (b) Determine the distance from the base of the building that the projectile lands. (c) Determine the horizontal and vertical components of the velocity just before the projectile reaches the ground.

(a) 3.35 s (b) 78.4 m (c) vhorizontal = 23.4 m/s, vvertical = 32.8 m/s

Vector A is 5.5 cm long and points along the x axis. Vector B is 7.5 cm long and points at +30e to the negative x axis. (a) Determine the x and y components of Vector A . (b) Determine the x and y components of Vector B. (c) Determine the sum of these two vectors in terms of components. (d) Determine the sum of these two vectors in terms of magnitude and direction.

(a) Ax = 5.5 cm, Ay = 0 (b) Bx = -6.5 cm, By = 3.8 cm (c) Rx = -1.0 cm, Ry = 3.8 cm (d) 3.9 cm at 75e above -x axis

A 400-m tall tower casts a 600-m long shadow over a level ground. At what angle is the Sun elevated above the horizon? A) 34e B) 42e C) 48e D) can't be found; not enough information

A

A ball is thrown with a velocity of 20 m/s at an angle of 60e above the horizontal. What is the horizontal component of its instantaneous velocity at the exact top of its trajectory? A) 10 m/s B) 17 m/s C) 20 m/s D) zero

A

A fighter plane moving 200 m/s horizontally fires a projectile with speed 50.0 m/s in a forward direction 30.0e below the horizontal. What is the speed of the projectile with respect to a stationary observer on the ground? A) 245 m/s B) 250 m/s C) 268 m/s D) 293 m/s

A

A plane flying horizontally at a speed of 50.0 m/s and at an elevation of 160 m drops a package. Two seconds later it drops a second package. How far apart will the two packages land on the ground? A) 100 m B) 162 m C) 177 m D) 283 m

A

A plane is flying due South (270e) at 500 km/h. A wind blows from East to West (180e) at 45.0 km/h. Find the plane's velocity with respect to the ground. A) 502 km/h at 265e B) 502 km/h at 85e C) 520 km/h at 5e D) 545 km/h at 265e

A

A soccer ball is kicked with a velocity of 25 m/s at an angle of 45e above the horizontal. What is the vertical component of its acceleration as it travels along its trajectory? A) 9.80 m/s2 downward B) (9.80 m/s2) ˛ sin (45e) downward C) (9.80 m/s2) ˛ sin (45e) upward D) (9.80 m/s2) upward

A

If you walk 6.0 km in a straight line in a direction north of east and you end up 2.0 km north and several kilometers east. How many degrees north of east have you walked? A) 19e B) 45e C) 60e D) 71e

A

Ignoring air resistance, the horizontal component of a projectile's acceleration A) is zero. B) remains a non-zero constant. C) continuously increases. D) continuously decreases.

A

Three forces, each having a magnitude of 30 N, pull on an object in directions that are 120e apart from each other. Make a statement concerning the resultant force. A) The resultant force is zero. B) The resultant force is greater than 30 N. C) The resultant force is equal to 30 N. D) The resultant force is less than 30 N.

A

Three vectors, expressed in Cartesian coordinates, are x comp y comp S -3.5 +4.5 T 0 -6.5 U +5.5 -2.5 What is the magnitude of the resultant vector S + T + U ? A) 4.9 B) 24 C) 16 D) 18

A

Which of the following is an accurate statement? A) A vector cannot have zero magnitude if one of its components is not zero. B) The magnitude of a vector can be less than the magnitude of one of its components. C) If the magnitude of vector A is less than the magnitude of vector B, then the x-component of A is less than the x-component of B. D) The magnitude of a vector can be positive or negative.

A

Which of the following operations will not change a vector? A) Translate it parallel to itself. B) Rotate it. C) Multiply it by a constant factor. D) Add a constant vector to it.

A

Your motorboat can move at 30 km/h in still water. How much time will it take you to move 12 km downstream, in a river flowing at 6.0 km/h? A) 20 min B) 22 min C) 24 min D) 30 min

A

A ball is thrown at an original speed of 8.0 m/s at an angle of 35e above the horizontal. What is the speed of the ball when it returns to the same horizontal level? A) 4.0 m/s B) 8.0 m/s C) 16 m/s D) 9.8 m/s

B

A pilot drops a bomb from a plane flying horizontally at a constant speed. Neglecting air resistance, when the bomb hits the ground the horizontal location of the plane will A) be behind the bomb. B) be over the bomb. C) be in front of the bomb. D) depend on the speed of the plane when the bomb was released.

B

A projectile is launched with an initial velocity of 60.0 m/s at an angle of 30.0e above the horizontal. What is the maximum height reached by the projectile? A) 23 m B) 46 m C) 69 m D) 92 m

B

A stone is thrown horizontally from the top of a tower at the same instant a ball is dropped vertically. Which object is traveling faster when it hits the level ground below? A) It is impossible to tell from the information given. B) the stone C) the ball D) Neither, since both are traveling at the same speed.

B

An airplane with a speed of 120 km/h is headed 30.0e east of north in a wind blowing due west at 30.0 km/h. What is the speed of the plane relative to the ground? A) 90.0 km/h B) 110 km/h C) 137 km/h D) 150 km/h

B

If a ball is thrown with a velocity of 25 m/s at an angle of 37e above the horizontal, what is the vertical component of the velocity? A) 12 m/s B) 15 m/s C) 19 m/s D) 25 m/s

B

Ignoring air resistance, the horizontal component of a projectile's velocity A) is zero. B) remains constant. C) continuously increases. D) continuously decreases.

B

On a calm day (no wind), you can run a 1500-m race at a velocity of 4.0 m/s. If you ran the same race on a day when you had a constant headwind which slows your speed by 2.0 m/s, the time it would take you to finish would be A) 250 s. B) 750 s. C) 1125 s. D) 9000 s.

B

The driver of a motorboat that can move at 10 m/s in still water wishes to travel directly across a narrow strait in which the current flows at 5.0 m/s. At what angle upstream should the driver head the boat? A) 27e B) 30e C) 60e D) 63e

B

Two displacement vectors have magnitudes of 5.0 m and 7.0 m, respectively. When these two vectors are added, the magnitude of the sum A) is 2.0 m. B) could be as small as 2.0 m, or as large as 12 m. C) is 12 m. D) is larger than 12 m.

B

Two forces are acting on an object as shown in Fig. 3-1. What is the magnitude of the resultant force? A) 47.5 N B) 185 N C) 198 N D) 200 N

B

Two vectors A and B have components (0, 1) and (-1, 3), respectively. What are the components of the sum of these two vectors? A) (1, 4) B) (-1, 4) C) (1, 2) D) (-1, 2)

B

When a football in a field goal attempt reaches its maximum height, how does its speed compare to its initial speed? A) It is zero. B) It is less than its initial speed. C) It is equal to its initial speed. D) It is greater than its initial speed.

B

Which one of the following is an example of a vector quantity? A) distance B) velocity C) mass D) area

B

You are traveling at 55 mi/h in the +x axis relative to a straight, level road and pass a car traveling at 45 mi/h. The relative velocity of your car to the other car is A) -10 mi/h. B) 10 mi/h. C) 65 mi/h. D) 35 mi/h.

B

A ball thrown horizontally from a point 24 m above the ground, strikes the ground after traveling horizontally a distance of 18 m. With what speed was it thrown? A) 6.1 m/s B) 7.4 m/s C) 8.1 m/s D) 8.9 m/s

C

A bullet is fired horizontally, and at the same instant a second bullet is dropped from the same height. Ignore air resistance. Compare the times of fall of the two bullets. A) The fired bullet hits first. B) The dropped bullet hits first. C) They hit at the same time. D) cannot tell without knowing the masses

C

A butterfly moves with a speed of 12.0 m/s. The x component of its velocity is 8.00 m/s. The angle between the direction of its motion and the x axis must be A) 30.0e. B) 41.8e. C) 48.2e. D) 53.0e.

C

A car travels 20 km West, then 20 km South. What is the magnitude of its displacement? A) 0 km B) 20 km C) 28 km D) 40 km

C

A girl throws a rock horizontally, with a velocity of 10 m/s, from a bridge. It falls 20 m to the water below. How far does the rock travel horizontally before striking the water? A) 14 m B) 16 m C) 20 m D) 24 m

C

A jumper in the long-jump goes into the jump with a speed of 12 m/s at an angle of 20e above the horizontal. How far does the jumper jump? A) 3.4 m B) 6.2 m C) 9.4 m D) 15 m

C

A jumper in the long-jump goes into the jump with a speed of 12 m/s at an angle of 20e above the horizontal. How long is the jumper in the air before returning to the Earth? A) 0.21 s B) 0.42 s C) 0.84 s D) 1.3 s

C

A package of supplies is dropped from a plane, and one second later a second package is dropped. Neglecting air resistance, the distance between the falling packages will A) be constant. B) decrease. C) increase. D) depend on their weight.

C

A plane has an air speed of 200 m/s due North, and is in a wind of 50.0 m/s to the West. The plane's speed relative to the ground is A) 150 m/s. B) 200 m/s. C) 206 m/s. D) 250 m/s.

C

At what angle should a water-gun be aimed in order for the water to land with the greatest horizontal range? A) 0e B) 30e C) 45e D) 60e

C

If the acceleration of an object is always directed perpendicular to its velocity, A) the object is speeding up. B) the object is slowing down. C) the object is turning. D) this situation would not be physically possible.

C

If the acceleration vector of an object is directed anti-parallel to the velocity vector, A) the object is turning. B) the object is speeding up. C) the object is slowing down. D) the object is moving in the negative x-direction.

C

In the diagram shown, the unknown vector is Diagram 1 A) A + B . B) A - B . C) B - A . D) A X B .

C

The acceleration of gravity on the Moon is only one-sixth of that on Earth. If you hit a baseball on the Moon with the same effort (and at the speed and angle) that you would on Earth, the ball would land A) the same distance away. B) one-sixth as far. C) 6 times as far. D) 36 times as far.

C

The driver of a motorboat that can move at 10 m/s in still water wishes to travel directly across a river 1.6 km wide in which the current flows at 5.0 m/s. How long will it take to cross the river? A) 5.3 min B) 2.7 min C) 2.4 min D) 1.8 min

C

Two vectors, of magnitudes 20 and 50, are added. Which one of the following is a possible answer for the magnitude of the resultant? A) 10 B) 20 C) 40 D) 80

C

Vector A = (1, 3). Vector B = (3, 0). Vector C = A + B . What is the magnitude of C ? A) 3 B) 4 C) 5 D) 7

C

A boat, whose speed in still water is 8.0 m/s, is directed across a river with a current of 6.0 m/s. What is the speed of the boat as it crosses the river? A) 5.3 m/s B) 6.0 m/s C) 8.0 m/s D) 10.0 m/s

D

A projectile is launched with an initial velocity of 60.0 m/s at an angle of 30.0e above the horizontal. How far does it travel? A) 152 m B) 160 m C) 184 m D) 318 m

D

A runner runs halfway around a circular path of radius 10 m. What is the displacement of the jogger? A) 0 B) 5 m C) 10 m D) 20 m

D

A stone is thrown horizontally with an initial speed of 10 m/s from the edge of a cliff. A stop watch measures the stone's trajectory time from the top of the cliff to the bottom to be 4.3 s. What is the height of the cliff? A) 22 m B) 43 m C) 77 m D) 91 m

D

An Olympic athlete throws a javelin at four different angles above the horizontal, each with the same speed: 30e, 40e, 60e, and 80e. Which two throws cause the javelin to land the same distance away? A) 30e and 80e B) 40e and 60e C) 40e and 80e D) 30e and 60e

D

If vector A = (-3.0, -4.0) and vector B = (+3.0, -8.0), what is the magnitude of vector C = A - B ? A) 13 B) 16 C) 144 D) 7.2

D

The resultant of two vectors is the smallest when the angle between them is A) 0e. B) 45e. C) 90e. D) 180e.

D

Three vectors, expressed in Cartesian coordinates, are x comp y comp S -3.5 +4.5 T 0 -6.5 U +5.5 -2.5 What is the angle of the resultant vector S + T + U measured from the positive x axis? A) 24e above B) 24e below C) 66e above D) 66e below

D

Two forces are acting on an object as shown in Fig. 3-1. What is the direction of the resultant force? A) 12e above -x B) 78e above -x C) 12e above +x D) 78e above +x

D

Two vectors A and B have components (0, 1) and (-1, 3), respectively. What is magnitude of the sum of these two vectors? A) 2.8 B) 3.2 C) 3.9 D) 4.1

D

Vector A has magnitude 8.0 m at an angle of 30 degrees below the +x axis. The y component of A is A) 6.9 m. B) -6.9 m. C) 4.0 m. D) -4.0 m.

D

You are throwing a ball for the second time. If the ball leaves your hand with twice the velocity it had on your first throw, its horizontal range R (compared to your first serve) would be A) 1.4 times as much. B) half as much. C) twice as much. D) four times as much.

D

You are trying to cross a river that flows due south with a strong current. You start out in your motorboat on the east bank desiring to reach the west bank directly west from your starting point. You should head your motorboat A) due west. B) due north. C) in a southwesterly direction. D) in a northwesterly direction.

D

A projectile is fired from ground level with an initial speed of 55.6 m/s at an angle of 41.2e above the horizontal. (a) Determine the time necessary for the projectile to reach its maximum height. (b) Determine the maximum height reached by the projectile. (c) Determine the horizontal and vertical components of the velocity vector at the maximum height. (d) Determine the horizontal and vertical components of the acceleration vector at the maximum height.

a) 3.73 s (b) 68.3 m (c) vhorizontal = 41.8 m/s, vvertical = 0 (d) ahorizontal = 0, avertical = -9.8 m/s2

Vector A is 75.0 cm long and points at 30e above the positive x axis. Vector B is 25.0 cm long and points along the negative x axis. Vector C is 40.0 cm long and points at 45e below the negative x axis. (a) Determine the x and y components of Vector A . (b) Determine the x and y components of Vector B . (c) Determine the x and y components of Vector C . (d) Determine the sum of these three vectors in terms of components. (e) Determine the sum of these three vectors in terms of magnitude and direction.

a) Ax = 65 cm, Ay = 38 cm (b) Bx = -25 cm, By = 0 (c) Cx = 21 cm, Cy = -21 cm (d) Rx = 61 cm, Ry = 17 cm (e) 63 cm at 20e above x axis