- #1
Chris0101
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Homework Statement
Four blocks of masses 20kg, 30kg, 40kg, and 50kg are stacked on top of one another in an elevator in order of decreasing mass with the lightest mass on the top of the stack. The elevator moves downward with an acceleration of ##3.2m/s^2## . Find the contact force between the 30kg and 40kg masses.
Homework Equations
Newton's second law:
##F = ma##
In the case of the question at hand:
##F = mg + ma##
The Attempt at a Solution
Due to the fact that the elevator is moving downward with a positive acceleration, the total force that the top two blocks apply onto the 40kg block will be:
##F = mg + ma##
##F = (50kg)(9.81m/s^2) + (50kg)(3.2m/s^2)##
##F = 490.5N + 160.0N##
##F = 650.5N##
This shows that the force acting on the 40 kg block from the top two blocks (20kg & 30kg) is 650.5N. This downward magnitude of force is the amount of force that the 40kg block has to support which is also the normal force that the 40kg block. With that, the contact force between the 30kg and 40kg block is 650.5N
I'm not sure if this is correct. If someone can correct me on this question that would be great. Thanks for the help.