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72 Speed DS

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72 Speed DS

by ern5231 » Sun Oct 04, 2009 6:03 am
Q1)A, B are 100m above the ground and B is dropped 10 sec before A. Which one first reaches the ground?

1) B is 25% faster than A
2) A's speed is greater than 2 m/s

Q2)Lift A and B are 200 feet above the ground, two elevators have a constant rate of decline. B declines 10 sec later than A. Which one first reaches the ground?

I: B's speed is 1 feet / s more than that of A

II: B's speed is 25% more than that of
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Re: 72 Speed DS

by umaa » Sun Oct 04, 2009 6:46 am
ern5231 wrote:Q1)A, B are 100m above the ground and B is dropped 10 sec before A. Which one first reaches the ground?

1) B is 25% faster than A
2) A's speed is greater than 2 m/s

Q2)Lift A and B are 200 feet above the ground, two elevators have a constant rate of decline. B declines 10 sec later than A. Which one first reaches the ground?

I: B's speed is 1 feet / s more than that of A

II: B's speed is 25% more than that of
Q1: IMO A

Q2: IMO C

Oa pls
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by ern5231 » Thu Oct 08, 2009 7:52 pm
Your answers are correct. Can you please give explanations?
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Re: 72 Speed DS

by fruti_yum » Mon Nov 02, 2009 2:34 pm
umaa wrote:
ern5231 wrote:Q1)A, B are 100m above the ground and B is dropped 10 sec before A. Which one first reaches the ground?

1) B is 25% faster than A
2) A's speed is greater than 2 m/s

Q2)Lift A and B are 200 feet above the ground, two elevators have a constant rate of decline. B declines 10 sec later than A. Which one first reaches the ground?

I: B's speed is 1 feet / s more than that of A

II: B's speed is 25% more than that of
Q1: IMO A

Q2: IMO C

Oa pls

I dont understand why question 2 is C. IMO B
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Re: 72 Speed DS

by life is a test » Tue Nov 03, 2009 6:56 am
fruti_yum wrote:
umaa wrote:
ern5231 wrote:Q1)A, B are 100m above the ground and B is dropped 10 sec before A. Which one first reaches the ground?

1) B is 25% faster than A
2) A's speed is greater than 2 m/s

Q2)Lift A and B are 200 feet above the ground, two elevators have a constant rate of decline. B declines 10 sec later than A. Which one first reaches the ground?

I: B's speed is 1 feet / s more than that of A

II: B's speed is 25% more than that of
Q1: IMO A

Q2: IMO C

Oa pls
to answer this question we need to know the actual speeds of both lifts to work out if the 10secs lag is reversed because of a difference in speed:

B only tells us that B is faster than A but we dont know whether or not the speed advantage is enough to overcome the 10 sec lag.

combining the statement tells us that 1f/s = 25% hence 100% = 4 so A's speed is 4f/s and B's speed is 5f/s which is sufficient to work out the actual times they reach the bottom.

hope that helps.




I dont understand why question 2 is C. IMO B
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