Stockroom worker pushes a box homework problem

AI Thread Summary
To determine the horizontal force needed to maintain the motion of a box being pushed at a constant speed, it's important to recognize that constant velocity implies zero acceleration. The force of friction, calculated using the coefficient of kinetic friction and the normal force, equals the applied force required to keep the box moving. In this case, the normal force is 109.76 N, leading to a frictional force of approximately 21.95 N. Therefore, the worker must apply a horizontal force of 21.95 N to maintain the box's motion. Understanding the relationship between force, friction, and acceleration is crucial in solving this problem.
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Homework Statement



A stockroom worker pushes a box with mass 11.2 kg on a horizontal surface with a constant speed of 3.50m/s. The coefficient of kinetic friction between the box and the surface is .20. What horizontal force must the worker apply to maintain the motion?

Homework Equations



F=ma
F=\muN


The Attempt at a Solution


First I drew my free body diagrams of course and found my Normal force to be 109.76N. Then i used this number and plugges it into F=ma(F=11.2x3.5) and got 39.2. Then using the 2nd equation above I found F=21.95. I was not sure if i was doing it correctly but then i added the 39.2+21.95= 61.152 as my F and answer. But I realized this cannot be right because i used 3.5 as my acceleration when it is just a constant velocity so I do not know how to even approach this question... PLEASE HELP!
 
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If velocity is constant than all forces are equal. Force of friction will equal the applied force. Just do Force friction= normal fprce x coeddicient of kinetic friction. Since forces are equal they will be the same value.
 
Thread 'Variable mass system : water sprayed into a moving container'

Thread 'Variable mass system : water sprayed into a moving container'

Starting with the mass considerations #m(t)# is mass of water #M_{c}# mass of container and #M(t)# mass of total system $$M(t) = M_{C} + m(t)$$ $$\Rightarrow \frac{dM(t)}{dt} = \frac{dm(t)}{dt}$$ $$P_i = Mv + u \, dm$$ $$P_f = (M + dm)(v + dv)$$ $$\Delta P = M \, dv + (v - u) \, dm$$ $$F = \frac{dP}{dt} = M \frac{dv}{dt} + (v - u) \frac{dm}{dt}$$ $$F = u \frac{dm}{dt} = \rho A u^2$$ from conservation of momentum , the cannon recoils with the same force which it applies. $$\quad \frac{dm}{dt}...
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