An object started to move from its starting point with the initial velocity of 3.6 m/s to the right and constant decelerating at 1.2 m/s. What is the velocity and displacement when time is 1 sec? 2 secs? 3 secs? 4 secs? 5 secs? 6 secs?

1 Answer
Richard G. · Stefan V.
Oct 11, 2015

After one second: #d = "3.0 m"#

Explanation:

The displacement calculation is different from the #v_"final"# calculation

#v_"final" = v_"initial" + "acceleration" xx "time"#

#"diplacement" = v_"initial" xx "time" + 1/2 xx "acceleration" xx "time"^2#

Notice that the acceleration is opposite direction to the initial velocity, so we show it as negative.

So:

#d_"1 sec" = 3.6"m"/cancel("s") xx 1cancel("s") + 1/2 xx (-1.2"m"/cancel("s"^2) xx 1^2cancel("s"^2))#

# = "3.6 m" + (-"0.6 m")#

#= "3.0 m" -># after 1 second

and:

#d_"2 sec" = 3.6 "m"/cancel("s") xx 2 cancel("s") + 1/2 xx ( -1.2"m"/cancel("s"^2) xx 2^2cancel("s"^2))#

#= "7.2 m" + ( -"2.4 m")#

#= "4.8 m" -># after 2 seconds

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