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What's the net force?

A person pushes a block of mass M=6.0 kg with a constant speed of 5.0 m/s straight up a flat surface inclined 30 degrees above the horizontal. The coefficient of kinetic friction between the block and the surface is μ=0.40. What's the net force acting on the block?
Answer: 0 N

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Robert J. | Certified High School AP Calculus and Physics TeacherCertified High School AP Calculus and Ph...
4.6 4.6 (13 lesson ratings) (13)
Check Marked as Best Answer
Apply Newton's second law.
Since a = 0, by Newton's second law,
Fnet = ma = 0 N
Amarjeet K. | Professional Engineer for Math and Science TuroringProfessional Engineer for Math and Scien...
4.6 4.6 (8 lesson ratings) (8)
Check the question again. I think the following is the intent of the question:
Force due to wt of block acting downward along the inclined surface = 6 x 10 sin(30) = 30N
Force due to friction acting downward along the inclined surface = 0.4 x 6 x 10 cos(30) = 20.78N
Net force acting downwards ~ 30 + 20 = 50N
If external force applied = 50N then block will be stationary
In order for the block to move exyternal force must be more than 50N. Once the block begins to move a constant 50N of force will be required to keep the blcok moving with a constant speed.