Really hard physics problem?
2018-07-26 3:24 pm
Initially there is a man standing in the middle of a rod of 2 m. Both ends of the rod are hanged on the ceiling by strings which will break if the tension is greater than 400N. The man is 50kg and he starts to move to the right. which string will break first, and how far must the man move to the right for one of the strings to break?
回答 (2)
2018-07-27 12:07 pm
FL = Force on the string on Left
FR = Force on the string on Right
FL+FR=weight of man=50*9.8=490N
As man move right, d = man from Right string
Using moment formula, pivot on the Left end of the rod:
FR x 2m = 490N x (2m - d)
Sting break if F on string >400N, so
400N x 2 < 490 (2-d)
d < 0.4m at right end.
Then calculate the force on the left string
FL=490-400=90N to be less than FR. (common sense)
Answer is A for the right string to break first.
Be aware the question defined the man moves to the right... so the right string at closer than 0.4m will break first.
If the man is allow to move to the left, the left string will break first at closer than 0.4m at left. Thus Answer C is NOT the correct answer.
The other two answer as both strings will be less than the limit, so no break anyhow.
FR = Force on the string on Right
FL+FR=weight of man=50*9.8=490N
As man move right, d = man from Right string
Using moment formula, pivot on the Left end of the rod:
FR x 2m = 490N x (2m - d)
Sting break if F on string >400N, so
400N x 2 < 490 (2-d)
d < 0.4m at right end.
Then calculate the force on the left string
FL=490-400=90N to be less than FR. (common sense)
Answer is A for the right string to break first.
Be aware the question defined the man moves to the right... so the right string at closer than 0.4m will break first.
If the man is allow to move to the left, the left string will break first at closer than 0.4m at left. Thus Answer C is NOT the correct answer.
The other two answer as both strings will be less than the limit, so no break anyhow.
2018-07-26 3:26 pm
The answers are
A: Right 0.4m
B: Right 0.6m
C: Left 0.4m
D: Left 0.6m
A: Right 0.4m
B: Right 0.6m
C: Left 0.4m
D: Left 0.6m
收錄日期: 2021-04-11 21:56:51
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