# A simple motion question ?

1. Jan 8, 2012

### MsTech

1. The problem statement, all variables and given/known data
A lorry of a mass 1500kg increases its velocity from 12m/s to 20m/s.

2. Relevant equations
a) calculate the change in momentum of the lorry.
b) The time taken for this change in velocity id 2 minutes. Calculate the average resultant force applied on the lorry.

3. The attempt at a solution
I worked out part a) by using the formula momentum= mv and got the ans 12000kgm/s
but i dont know how to work out part b.
Does anyone know how ?

2. Jan 8, 2012

### Staff: Mentor

Look up the impulse-momentum theorem.

3. Jan 8, 2012

### MsTech

Thank you so the formula is that ? F⃗ Δt=Δp⃗ =m(v⃗ f−v⃗ i)
So the Force= mass (velocity * f orce - velocity* impulse)?

4. Jan 8, 2012

### Staff: Mentor

Not exactly. Impulse = FΔt. The impulse momentum theorem states that the impulse will equal the change in momentum:

FΔt = Δ(mv) = m Δv

5. Jan 8, 2012

### MsTech

Ah i tought it didn't make sense ! Ok got it ! thanks a lot :-)