# What is its velocity at t=6s?

0

The figure shows the force acting on a 2.0 kg object as it moves along the x-axis. The object is at rest at the origin at t= 0 s.

http://session.masteringphysics.com/problemAsset/1…

I know the acceleration is 0 but im having trouble with the velocity.

thats wrong.

• Since F=ma we can get acceleration on the object by a=F/m

From t=0 sec to t=3 sec, a=4/2=2 m/s^2

From t=3 sec to t=5 sec, a=-2/2=-1 m/s^2

From t=5 sec on, a=0 m/s^2

Use velocity from constant acceleration equation,

v=v0+at

break it down into the chunks where the acceleration changes, use the final velocity at that time, as the inital velocity for the next acceleration.

At t=0, v=0, at t=3, v=0+2*(3)=6 m/sec

At t=5 sec, v=6+(-1)(5)=6-5=1 m/sec

• Let’s work this in parts…

part 1 time 0 to 3 seconds

F = m * a then a = 4/2= 2 m/s^2

Vf = Vo + at therefore Vf= 2*3 = 6 since Vo =0

part 2 3 to 5 seconds

vf last part is Vo on this part

Vo = 6

a = – 1

t= 2

Vf = Vo + at

Vf = 6 – 2 = 4

last part

5 to 6 seconds

Vo = 4 last vf is Vo on this part

t = 1

a= 0 there is no force

Vf = Vo + at

Vf = 4

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