Velocity as a function of force/impulse/time.

[the7joker7]

Homework Statement

The force shown in the force vs time diagram in Figure P6.11 acts on a 1.5 kg object. Find the impulse of the force, the final velocity of the object if it is initially at rest, and the final velocity if initial velocity is -2.00 m/s.

http://books.google.com/books?id=wD...x_cOMU0&sig=cqAzhugYbnZdpBwdwDdlRM82s1g&hl=en

Homework Equations

V^{2} = V_{0}^{2} + 2a\Deltax

The Attempt at a Solution

I know impulse is just 8 Newton seconds, and i know that's the right answer. But the 2nd question is getting me.

V^{2} = 0 + 2(2/1.5)(5) gives V^{2} = 13.33. so v = 3.65.

But the answer is v = 5.3.

Where did I go wrong?

 

[Shooting Star]

Homework Equations

V^{2} = V_{0}^{2} + 2a\Deltax

This is when accn is const, which here it's not.

The Attempt at a Solution

I know impulse is just 8 Newton seconds, and i know that's the right answer. But the 2nd question is getting me.

V^{2} = 0 + 2(2/1.5)(5) gives V^{2} = 13.33. so v = 3.65.

But the answer is v = 5.3.

Where did I go wrong?

Use impulse = change in momentum.

 

[Astronuc]

Shooting Star nailed this one.

Here's a good reference for the future.
http://hyperphysics.phy-astr.gsu.edu/hbase/impulse.html