Uniform Velocity
If a body is moving towards the right with a uniform velocity then the net force being applied to the body is
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3 solutions
Discussions for this problem are now closed
Hm ... this is assuming that the mass of the body stays constant ...
What happens if the body is losing mass?
why are you assuming there's no resistance it wasn't mentioned and there's no smooth surface , so segma F=ma , F-R=ma , F=R , the forces just cancels the resistance force of the surface or the ground so the body moves with uniform velocity . This is actually a case , the problem is not well stated
If the body is losing or gaining mass only the magnitude of the net force changes, not the direction.
In this case, the question is asking for the direction, ie right, left or 0. It actually matters what is happening to the mass.
We actually have force as the rate of change of momentum, or F = d t d m v .
if the velocity is constant, then F = v ⋅ d t d m . Hence, if the mass is increasing, then the net force applied is positive, hence acting right (we need force to maintain uniform velocity). Similarly, if the mass is decreasing, then the net force applied is negative, hence acting left.
Note: In the case where mass is constant, then F = m d t d v = m a , which the the formula that we love so much.
@Calvin Lin – simply you can say that velocity is constant, derivative of constant is zero hence acceleration is zero, so the force will be zero.
@Calvin Lin – I think it'd be better if the question mentioned us to neglect friction, since if we consider the frictional force acting here, the net external force acting on the body,i.e., F ext = 0 when the body is in motion. In that case, the force acting on the body could be said to be constant when the body is in motion and 0 iff the body is at rest.
@Calvin Lin – It didn't occur to me that push ( in the direction of motion) would need to change direction if mass were decreasing and velocity maintained. Thanks
@Calvin Lin – "Net Force" got the best of me
why are you assuming there's no resistance it wasn't mentioned and there's no smooth surface , so segma F=ma , F-R=ma , F=R , the forces just cancels the resistance force of the surface or the ground so the body moves with uniform velocity . This is actually a case , the problem is not well stated
Two words, net force.
Are we neglecting friction
Whether we neglect friction or not, answer is still same.
It never stated that friction was neglected, and or the mass is constant, so the answer "none of the rest" is the only correct solution given the current problem statement.
Question doesn't say anything about change in mass, so we assumed that mass is constant, like how we often neglect air resistance in most of physics problems.
And ever within friction, we know that body moves with an uniform velocity, which means acceleration is 0. So net force has to be 0 according to Newton's second law of motion.
Since the body is having zero acceleration therefore no force is exerted on it !
Be careful... This is a similar to the mistake I made. Given the vagueness of the problem statement "no force" is not necessarily a correct statement. However, "Net force" (in the absence of varying mass) will always be consistent.
As there is a constant velocity, acceleration is equal to 0.
From F = m a , and substituting a=0, F must also equal 0
Therefore there is no net force being applied on the body.
Assuming that mass doesn't change. We then can apply Newton's second law of motion. F = m a
Since a body is moving with a uniform velocity, where both magnitude and direction of velocity do not change, acceleration is 0, hence net force is 0.