A woman living in a third-story apartment is moving out. Rather than carrying everything down the stairs, she decides to pack her belongings into crates, attach a frictionless pulley to her balcony railing, and lower the crates by rope. How hard must she pull on the horizontal end of the rope to lower a 25 kg crate at steady speed?

Explanation:

Let the force applied by her be T on the rope . This force will create tension in the rope. It will act in upper direction on the crates . The weight of the crate will act in downward direction .

Net force on the crate = mg - T in downward direction

Applying Newton's law

mg - T = m a

a =0 ( speed is steady )

mg - T = 0

T = mg

= 25 x 9.8

= 245 N

Force to be applied by her

= 245 N

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