A bob is suspended from a spring balance in an elevator. The reading is 100 N when lift is at rest. If the spring balance reading now changes to 80 N, then the elevator is moving
(1)upwards with increasing. speed
(2)downwards with increasing speed
(3)downwards with decreasing speed
(4)downwards with constant speed
Answers
Answered by
3
Answer:
4 is your answer. Thank you
Answered by
1
Answer:
(2)downwards with increasing speed
Explanation:
When lift is at rest reading is 100 N
mg = 100 N
Lets assume that elevator is moving up ward with acceleration a m/s².So the reading of spring balance ,S
S= mg + m a
S= 100 + m a
Given that
S= 80 N
80 = 100 - m a
m a = -20 N
It means that our assumption is wrong because we assume that acceleration is upward.But it comes out with negative sign .So we can say that elevator is moving downward.
When moving downward with acceleration a m/s²
S= mg - m a
80 = 100 - m a
m a = 20 N
Answer
(2)downwards with increasing speed
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