Chapter 5 Test
An airplane whose airspeed is 280 km/h flies parallel to the direction of a wind with a pseed of 50 km/h/. What are the two possible speeds of the plane relative to the ground?
Tailwind 280 km/h + 50 km/h = 330 km/h Headwind 280 km/h - 50 km/h = 230 km/h
In the absense of air friction, the angle at which a thrown ball will go the farthest is
45 degrees
A baseball is hurled into the air at an angle of 40 degrees above the horizontal and lands on a target that is at the same level as that where the baseball started. The baseball will also land on the target if it is thrown at an angle of
50 degrees it adds up to 90
A ball is thrown upward. Its initial vertical component of velocity is 30 m/s and its initial horizontal component is 10 m/s. What is the ball's speed 1.0 s later?
0 s- 30m 1s- 20 m 2s - 10 m 3s - 0 m speed = 22.26 m/s 20 2 + 20 2 = R2 500 = R2 10 square root 5 = R 10 2 + 30 2 = R2 1000 = R2 = 10 square root 10 or 31.6
What representing velocity as a vector:
-The direction of the arrow shows the direction of motion (ORIENTATION) -The length of the arrow represents speed (magnitude) -the length of the arrow is drawn to a suitable scale
An object is dropped and falls freely to the ground with an acceleration of g. If it is thrown upward at an angle instead, its acceleration would be
still g
A ball thrown into the air will never go as far as physics ideally would predict b/c ........
the air friction slows down the ball
After a rock thrown straight up reaches the top of its path and then falls a short distance, its acceleration is (neglect air resistance)
the same as it was at the top of the path (still g)
The horizontal compnent of a projectile's velocity is independent of ....
the vertical component of motion
T or F The vector sum is called the resultant
true
A snowball rolls off the edge of a horizontal roof at a velocity of 5.0 m/s. What is the speed of the snowball 1.0 s later?
v = g x t v=10 x 1 = 10m/s d = 1/2g x 1 2 d= 5 m
Consider an escalator at an angle at an angle of 45 degrees above the horizontal that moves with a velocity of 4.0 m/s. WHat is the horizontal component of the escalator's velocity?
vy = 2 square root 2 vs = 2 square root 2 m/s ... x2 + x2 = 42 2x/2 2 = 16 ---> square root x2 = square root 8 --> x = 2 square root 2
A projectile shot with an initial velocity of 60 m/s at an angle of 45 degrees follows a parabolic path and hits a stationary balloon at the top of its trajectory. With what speed does the projectile hit the balloon?
x2 + x2 = 60 2 x = 42.4 m/s square root vx2 + vy2
A projectile launched horizontally hits the ground in .4 seconds. If it had been launched with a much higher speed in the same direction, it would have hit the ground (neglecting Earth's curvature and air resistance) in
0.4 seconds
Which best approximates the resultant of a pair of 10-unit vectors at right angles to each other?
10 square root 2 but the best answer is 14.14 pr 14 units (102 + 102 = c2)
What is the resultant of a 6 unit vector and a 8 unit vector at right angles to each other?
10 units (62 + 82 =R2 or C2)
Suppose a small plane can fly at 110 km/h relative to the surrounding air. Suppose also that there is a 40 km/h tailwind. How fast does the plane's shadow move across the ground?
110 + 40 = 150 km/h
In the absence of air resistance, at what angle will a thrown ball go the same distance as one thrown at an angle of 65 degrees?
25 degrees
A ball is thrown upward. Its initial vertical component of velocity is 30 m/s and its initial horizontal component is 10 m/s. What is the ball's speed 4.0 s later?
30 m/s - 0 s 20 m/s - 1 s 10 m/s - 2 s 0 m/s - 3 s 10 m/s - 4 s Speed = 14.14 m/s downward 10 2 + 10 2 = R2 square root 200 = square root R2 10 square root 2
A motoboat is driven across a river at 4.0 km/h at right angles to a current that is flowing at 12 km/h. What is the resulting speed of the motorboat?
4 2 + 12 2 = R2 16 + 144 = R2 square root 160 = square root R2 12.6 = R
A cannon is launched horizontally from a tower. If the cannon has a barrel velocity of 50 m/s, where will the cannonball be 1 second later? (neglect air resistance)
50 m, d= sxt = 50m/s x 1s = 50m
A cannonball is launched from the ground at an angle of 30 degrees above the horizontal and a speed of 50 m/s. Ideally (no air resistance) the ball will land on the ground with a speed of
50 m/s
A ball will go the farthest if thrown almost horizontally
False, at 45 degrees it will go the farthest
T or F In the absense of air friction, the vertical component of a projectile's velocity doesn't change as the projectile moves.
False, the force of gravuty still acts on the vertical component
T or F: A single vector can be replaced by two vectors in the x and y directions that are at right angles to each other. These two x and y vectors are called the resultants of the original vector
False, they are components
Can a scalar quantity be made into a vector quantity by adding a direction to its magnitude? Explain why or why not and give an example.
Not always b/c if you add north to 9 kg, it would be 9kg north and that does not make any sense
A cannonball is fired at some angle into the air. In the first second it moves 5 meters horizontally. Assuming it doesn't hit the ground and air resistance is negligable, how far does it move horizontally in the next second?
The same as the first second. --> 5 meters
At the instant a ball is thrown horizontally with a large force, an identical ball is dropped from the same height. Which ball hits the ground first?
They hit the ground at the same time
T or F In the absense of air friction, the horizontal component of a projectile's velocity doesn't change as the projectile moves
True
T or F The velocity of the airplane is the sum of the airplane's velocity relative to the air and the wind's velocity relative to the ground.
True
What statement about projectiles are true?
a projectile moves through air or space a projectile is subject to the force of gravity a projectile in air is subject to air resistance
A scalar quantity is...
a quantity that can be described by magnitude only and has no direction
A vector quanity is...
any physical quanity that has both magnitude and direction, such as velocity acceleration or force
At what part of a path does a projectile have minimum speed?
at the top of the projectile
Kyle throws a ball horizontally from the top of a building that is 5.0 m high. He hopes the ball will reach a swimming pool that is at the bottom of the building, 10.0 m horizontally from the edge the building. If the ball is to reach the pool, with what initial speed must Kyle throw it with?
d = 1/2 gt2 5/5 = 5t2/5 square root 1 = square root t2 t=15 ..... 52 + 102 = R2 R = 11.18 m s =d/t = 11.18 m/1s =11.2 m/s
A cannon with a barrel velocity of 120 m/s launches a cannonball horizontally from a tower. Neglecting air resistance, how far vertically will the cannonball have fallen after 3 seconds?
d = 1/2 gt2 = 1/2g x 3 2 = 45 m
A ball is thrown horizontally from the top of a tall cliff. Neglecting air drag, what vertical distance has the ball fallen 2.0 seconds later?
d = 1/2 gt2 = d=5(2)2 d=20 m
A package falls out of a helicopter that is traveling horizontally at 60 m/s. It falls into the water below 8.00 seconds later. Assuming no air resistance, what is the HORIZONTAL distance it travels while falling?
d = 2 x t = 60 m/5 x 80s = 480 m
The orientation of a vector shows its ........
direction
A projectile is fired horizontally in a vacuum. The projectile maintains its horizontal component of speed b/c it
does not have any horizontal forces acting on it
T of F When two angles at right angles, the resultant of the vectors is the algebraic sum of the two vectors,
false you have to use pythagoream theorum
T or F: A quantity that has both magnitude and direction is called a scalar quantity
false, it's a vector
An airplane flying into a head wind loses ground speed, and an airplane flying with the wind gains ground speed. If an airplane flies at right angles to the wind, then ground speed is
more (the resultant vector)
In chp 2, you learned about "hang time," the jumper's feet are off the ground in a vertical jump. If the jumper runs horizontally and has the same vertical component of takeoff velocity, hang time will be
no difference or same
A ball is thrown into the air at some angle. At the top of the ball's path, its velocity is .............
only the horizontal component
In a standing jump, the hang time of a certain athlete is .4 seconds. What is her hang time when she jumps the same height while moving?
same time - 0.4 seconds
A plane flies north at 210 km/h. At the same time, there is wind of 60 km/h from the west. Use both scaled diagram and pythagean theorem to find the resultant velocity of the plane. How closely do you answers agree?
scale drawing : 1 side : 6cm 2 side: 21cm resultant : 21.8 cm pythagorean theorum: 210 2 + 60 2 = R2 441000 + 3600 = R2 square root: 47,700 = R2 218.4 = R
