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A particle has an initial velocity of 9m/s due east and a constant accelaration of 2m/sec ^2 due west. the distance covered by the particle in the 5th second of its motion is?
a) 0
b)0.5
c)2
d) none of the above
HINT- answer is 0.5 but i keep getting 0. help me out please.
The displacement is indeed 0 but not the distance. the distance is 0.5
Actually the the car is changing the direction of motion at 4.5 seconds. As such b/w 4 and 5 second the displacement is 0 but still the car still covers some distance.
The distance the mod of displacement made by the car b/w 4 and 4.5 seconds + mod of the displacement b/w 4.5 and 5 second.
b/w 4 to 4.5 seconds => (9)(0.5)-(4.52-42)= 4.5-4.25= 0.25
b/w 4.5 to 4 seconds => (9)(0.5)-(52-4.52)= 4.5-4.75= -0.25
Displacement =0, Distance =0.5
Here the particle velocity will become zero in 4.5 seconds, as
V=U+at
0=9–2*t
t=4.5sec.
Displacement in the same period will be
v^2-U^2=2*a*S
-81=-2*S
S4.5=20.25m
Let us call the point of velocity being zero as Point A.
now body will start moving backwards,
displacement in next 0.5 sec from point A,
s=U*t+1/2*a*t^2
S0.5=1/2*(-2)*0.25= -0.25m
hence distance covered is 0.25 m
(-ve sign indicates body moved in backward direction. It is to be noted that displacement and distance are not to be confused to be same)
Distance traveled in 4 seconds
S4= 9*4+1/2*(-2)*4^2
S4=36–16=20 m
Thus,
distance covered in 5th second is
D= (S4.5+|S0.5|)-S4
D=20.25+0.25–20
D=0.5m
v=u+at0=9−2×tt=4.5sec
v2−u2=2as−81=2ss4.5=20.25m
s=ut+21at2s0.5=21(−2)(0.25)2=−0.25m
s4=9×4+21(−2)(4)2s4=36−16=20
D=(s4.5+∣s0.5∣−s4)=20.5+0.25−20=0.5
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