Asked by zoha
4 kg block rests on a smooth horizontal surface,upper surface of 4 kg is rough.A block of mass 2 kg is placed on its upper surface.The acceleration of upper block with respect to earth when 4 kg mass is pulled by a horizontal force of 30N?coefficient of static friction=0.8 and coefficient of kinetic friction=0.6 I have been working to solve this but not getting it as i do not know what is force of friction on 2 kg block .I know it is coefficient of friction divided by normal reaction but what would be normal reaction?
Answers
Answered by
Damon
We do not know yet if the top block slips.
First, assume it does not slip.
F = m a
30 = (4+2) a
a = 5 m/s^2
Now
How much force is required to accelerate the top block at 5 m/s^2?
F = 2 (5) = 10 N required
How much do we have?
Fnormal = m g = 2*9.81 = 19.62 N
so friction max = .8 * 19.62 = 15.7 N
But we only need 10 N to keep that top block stuck on the bottom one, so it does not slide and we are finished.
First, assume it does not slip.
F = m a
30 = (4+2) a
a = 5 m/s^2
Now
How much force is required to accelerate the top block at 5 m/s^2?
F = 2 (5) = 10 N required
How much do we have?
Fnormal = m g = 2*9.81 = 19.62 N
so friction max = .8 * 19.62 = 15.7 N
But we only need 10 N to keep that top block stuck on the bottom one, so it does not slide and we are finished.