Momentum Q: Determine Speed, Friction of Metal Bar

[Atran]

Homework Statement

... The object has a mass 2000 kg and the metal bar has a mass of 400.
The object strikes the bar at speed 6 m/s. It comes to rest on the bar without bouncing.
As a result of the collision, the bar is driven into the ground to a depth of 0.75 m
a) Determine the speed of the bar immediately after the object strikes it.
b) Determine the average frictional force exerted by the ground on the bar.

Homework Equations

The basic mechanics equations.

The Attempt at a Solution

a) p₁ + p₂ = 12000 kg m/s
v₂ = (12000/400) m/s = 30 m/s
In the book, the answer is 5 m/s.

b) No idea! I don't have a value of (a) or (t).

 

[p21bass]

For a: it's just conservation of momentum.

For b: how does force relate to momentum?