Newton's second law and direction of force

AI Thread Summary
The discussion focuses on a physics problem involving a particle that decelerates from a speed of 22.1 m/s to a stop due to a constant force of 12.6 N over a distance of 55.3 m. The direction of the force is opposite to the particle's motion. The calculated deceleration is approximately -4.416 m/s², leading to a time of about 5.004 seconds for the particle to stop. To find the mass of the particle, the equation F=ma is used, but there is confusion regarding the calculation. The alternative method suggested involves using the work-energy principle, specifically the equation 1/2*m*v² = F*d.
neutron star
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Homework Statement


A particle is traveling in a straight line at a constant speed of 22.1 m/s. Suddenly, a constant force of 12.6 N acts on it, bringing it to a stop in a distance of 55.3 m.


Homework Equations





The Attempt at a Solution



(a) What is the direction of the force?
perpendicular to the direction of the particle's motion
*opposite the direction of the particle's motion
the same as the direction of the particle's motion
none of the above

(b) Determine the time it takes for the particle to come to a stop.
___ s

(c) What is its mass?
___ kg

F=ma
V_f=0
V_f ^2 = V_i ^2 + 2a(X-X_i)
0^2=(22.1m/s)^2 + 2a(55.3m)
0=(22.1m/s)+at
 
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neutron star said:
F=ma
V_f=0
V_f ^2 = V_i ^2 + 2a(X-X_i)
0^2=(22.1m/s)^2 + 2a(55.3m)
0=(22.1m/s)+at


Yes so the deceleration is ? And the time taken is?
 
0=22.1m/s^2+2a(55.3)
-110.6a=488.41m/s
a=-4.416m/s

0=22.1m/s^2+(-4.416m/s)t
22.1m/s^2/4.416m/s=5.004s
t=5.004s

Is this right?

How do I get mass from this? F=ma right, so m=F/a or 12.6=m(-4.416)
or m=12.6/-4.416. But it doesn't seem to work...
 
Last edited:
c) Use 1/2*m*v^2 = F*d
 
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