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Question:

Problem about Newton's Laws?

A crane of mass M 1.00 · 10^4 kg lifts a wrecking ball of mass m 1200kg directly upward.Find the magnitude of the normal force exerted on the crane by the ground while the wrecking ball is moving upward at a constant speed of v 1.00 m/s.I'm confused because there is a constant speed, no acceleration, then how can i use the second law Fma?

Answer:

Excatly rightSo you can set a 0Therefore F(net) 0 and all the forces must sum to zeroSUM(F(i)) 0 What forces are on the crane? In this configuration, there are only three significant forces: F(ball) + F(gravity) + F(normal) 0 You can easily calculate the force on the ball and the force due to gravity leaving the normal force as a single unknown.

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