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Shay10825
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Kinematics Please Help!
Hi everyone! I really need help on these problems! I'm so confused . Sorry this post is so long and they are numbered weird.
6.) A rocket, initially at rest, is fired vertically with an upward acceleration of 10 m/s^2. At an altitude of .5 km, the engine of the rocket cuts off. What is the maximum altitude it achieves?
My work:
Vi= 0, a=10 m/s^2, d(or x) = 500 m
Now I'm stuck! I know you have to split it into 2 parts (one on the way up and one on the way down), and on the way down a=-9.8. But you don't know Vf or t so I don't know what to do.
ANSWER: 1 km
10.) A boy on a skate board skates off a horizontal bench at a velocity of 10 m/s. One tenth of a second after he leaves the bench to two significant figures the magnitude of his velocity and his acceleration are what?
My work:
Would you put the information into vectors? and if so how? Did they give enough information?
ANSWER: 10 m/s ; 9.8 m/s^2
13.) A juggler throws two balls to the same height so that one is at the halfway point going up when the other is at the halfway point coming down. At that point:
a. Their velocities and accelerations are equal.
b. Their velocities are equal but their accelerations are equal and opposite.
c. Their accelerations are equal but their velocities are equal and opposite.
d. Their velocities and accelerations are both equal and opposite.
e. Their velocities are equal to their accelerations.
How do you know that the answer is c?
14.) A particle starts from the origin at t=0 with a velocity of 8j m/s and moves in the xy plane with a constant acceleration of (4i + 2j) m/s^2. At the instant the x coordinate of the particle is 29 m, what is the value of its y coordinate?
My Work:
xi= 0 , Vix=0, ax=4, xf=29, Viy=8, ay=2, yf=?, Vfy=0
Vf^2 = Vi^2 + 2ad
0= 64+4d
-64=4d
d=-16
yf=-16
But this is not the correct answer :grumpy: ! It's not even close to any of the choices . ahhhhhhh!
ANSWER: 45 m
15.) A particle starts from the origin at t=0 with a velocity of 6i m/s and moves in the xy plane with a constant acceleration of (-2i + 4j) m/s^2. At the instant the particle achieves its maximum positive x coordinate, how far is it from the origin?
?
I don't know where to start. I don't understand how you would find this.
ANSWER: 20 m
16.) A ball is thrown horizontally from the top of a building .1 km high. The ball strikes the ground at a point 65 m horizontally away from and below the point of release. What is the speed of the ball just before it strikes the ground?
Answer: 47 m/s
17.) A rifle is aimed horizontally at the center of a large target 60 m away. The initial speed of the bullet is 240 m/s. What is the distance from the center of the target to the point where the bullet strikes the target?
You have 3 vectors that form a triangle and you need to find the third side. 60 is one side and 240 is the other. I found the angle between them to be 75.52. Then I used the law of cosines and found the third side to be 232.379. This is not even close to any of the choices .
ANSWER: 31 cm.
19.) A carnival Ferris wheel has a 15-m radius and completes five turns about its horizontal axis every minute. What is the acceleration of a passenger at his lowest point during the ride?
My Work:
ar= (V^2)/(r)
C= 30pi so v= [(5*30pi)/1 min]
V = 150 m / 60 s
so: ar=.027
ANSWER: 4.1 m/s^2
21.) Two cars are traveling around identical circular racetracks. Car A travels a constant speed of 20 m/s. Car B starts at rest and speeds up with constant tangential acceleration until its speed is 40 m/s. When car B has the same (tangential) velocity as car A, it is always true that:
a. it is passing car A
b. it has the same linear (tangential) acceleration as car A.
c. it has the same centripetal acceleration as car A.
d. it has the same total acceleration as car A.
e. it has traveled farther than car A since starting.
Why is the answer c?
Any help would be greatly appreciated
~Thanks
Hi everyone! I really need help on these problems! I'm so confused . Sorry this post is so long and they are numbered weird.
6.) A rocket, initially at rest, is fired vertically with an upward acceleration of 10 m/s^2. At an altitude of .5 km, the engine of the rocket cuts off. What is the maximum altitude it achieves?
My work:
Vi= 0, a=10 m/s^2, d(or x) = 500 m
Now I'm stuck! I know you have to split it into 2 parts (one on the way up and one on the way down), and on the way down a=-9.8. But you don't know Vf or t so I don't know what to do.
ANSWER: 1 km
10.) A boy on a skate board skates off a horizontal bench at a velocity of 10 m/s. One tenth of a second after he leaves the bench to two significant figures the magnitude of his velocity and his acceleration are what?
My work:
Would you put the information into vectors? and if so how? Did they give enough information?
ANSWER: 10 m/s ; 9.8 m/s^2
13.) A juggler throws two balls to the same height so that one is at the halfway point going up when the other is at the halfway point coming down. At that point:
a. Their velocities and accelerations are equal.
b. Their velocities are equal but their accelerations are equal and opposite.
c. Their accelerations are equal but their velocities are equal and opposite.
d. Their velocities and accelerations are both equal and opposite.
e. Their velocities are equal to their accelerations.
How do you know that the answer is c?
14.) A particle starts from the origin at t=0 with a velocity of 8j m/s and moves in the xy plane with a constant acceleration of (4i + 2j) m/s^2. At the instant the x coordinate of the particle is 29 m, what is the value of its y coordinate?
My Work:
xi= 0 , Vix=0, ax=4, xf=29, Viy=8, ay=2, yf=?, Vfy=0
Vf^2 = Vi^2 + 2ad
0= 64+4d
-64=4d
d=-16
yf=-16
But this is not the correct answer :grumpy: ! It's not even close to any of the choices . ahhhhhhh!
ANSWER: 45 m
15.) A particle starts from the origin at t=0 with a velocity of 6i m/s and moves in the xy plane with a constant acceleration of (-2i + 4j) m/s^2. At the instant the particle achieves its maximum positive x coordinate, how far is it from the origin?
?
I don't know where to start. I don't understand how you would find this.
ANSWER: 20 m
16.) A ball is thrown horizontally from the top of a building .1 km high. The ball strikes the ground at a point 65 m horizontally away from and below the point of release. What is the speed of the ball just before it strikes the ground?
Answer: 47 m/s
17.) A rifle is aimed horizontally at the center of a large target 60 m away. The initial speed of the bullet is 240 m/s. What is the distance from the center of the target to the point where the bullet strikes the target?
You have 3 vectors that form a triangle and you need to find the third side. 60 is one side and 240 is the other. I found the angle between them to be 75.52. Then I used the law of cosines and found the third side to be 232.379. This is not even close to any of the choices .
ANSWER: 31 cm.
19.) A carnival Ferris wheel has a 15-m radius and completes five turns about its horizontal axis every minute. What is the acceleration of a passenger at his lowest point during the ride?
My Work:
ar= (V^2)/(r)
C= 30pi so v= [(5*30pi)/1 min]
V = 150 m / 60 s
so: ar=.027
ANSWER: 4.1 m/s^2
21.) Two cars are traveling around identical circular racetracks. Car A travels a constant speed of 20 m/s. Car B starts at rest and speeds up with constant tangential acceleration until its speed is 40 m/s. When car B has the same (tangential) velocity as car A, it is always true that:
a. it is passing car A
b. it has the same linear (tangential) acceleration as car A.
c. it has the same centripetal acceleration as car A.
d. it has the same total acceleration as car A.
e. it has traveled farther than car A since starting.
Why is the answer c?
Any help would be greatly appreciated
~Thanks
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