With which force should a man pull on a 5kg block so that it moves at a constant speed of 20m/s, if the friction coefficient between the floor and the block is 0.2?

Question

anonymous · Answer

@rajathsbhat, hope you had a great weekend^^

shane_b · Answer

All you need to do is calculate the force of friction which is the normal force times the coefficient of friction:$$F_f=\mu_k mg=(0.2)(5kg)(9.8m/s^2)=9.8N$$If the block is to maintain a constant velocity, the man needs to pull on it with a force of 9.8N (in the opposite direction).

anonymous · Answer

i did that, but if it is to maintain a constant velocity of 20m/s doesn't that mean something?

shane_b · Answer

It doesn't matter what the velocity is...the concern is that you don't change it.  Since the above results in a net force of 0N, the object's velocity will not change.

anonymous · Answer

constant velocity the resultant force must be zero.the accelaration must be zero

anonymous · Answer

okay thank you @Shane_B

shane_b · Answer

This all goes back to Newton's first law btw.  
You welcome :)

shane_b · Answer

*you = you're!