Homework in physics (average force and momentum)

[yek_zzz]

Homework Statement

A 1000 kg car strikes a tree at 30 km/hr & comes to a stop in 0.15s. Find its initial momentum and the average force on the car while it is being stopped.


Attempt at a solution

For velocity,

I tried converting 30 km/hr to m/s

30 km/hr * 1hr/3600s*1000m/1km

=30000 m/ 3600 s = 8.33 m/s

For the momentum...

p = mv

p = 1000 kg (8.33 m/s)

p = 8330 kg * m/s

Is this correct? How do I find the average force? Please help me. My teacher says I'm wrong at some equation.

 

[Doc Al]

Everything you've done so far is correct. To find the average force, consider the impulse delivered by the tree.

 

[yek_zzz]

how do I solve for that? We are only given the mass, velocity and the time.

 

[Doc Al]

You have all you need. What's the definition of impulse? Look up the impulse-momentum theorem. You'll set up an equation and solve for the force.