An inventive child named Nick wants to reach an apple in a tree without climbing

Question

An inventive child named Nick wants to reach an apple in a tree without climbing the tree. Sitting in a chair connected to a rope that passes over a frictionless pulley, Nick pulls on the loose end of the rope with such a force that the spring scale reads 250 N. Nick's true weight is 320 N and the chair weighs 160 N. Nick's feet are off the ground.

A) Draw a diagram showing the forces on the chair.

B) Show that the acceleration of the chair is upward.

C) Find the magnitude of the acceleration of the chair.

D) Find the force Nick exerts on the chair.

Explanation / Answer

B) Had the chair been stationary, the sum of weights would have been equal to the reading of the balance.

Since the reading is lower than the sum, the chair is acceleration upward.

Total mass of chair and nick=(320+160)/9.8=49kg

Acceleration=(480-250)/49=4.7m/s2

Force exerted by Nick on the chair=F

F-mg=ma

F=473N

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