Force and Time in Collisions

Problems of this nature usually consider two equations:

I=Ft and;

I=\Delta P=mv-mu

Example 1:

20N force acts on a stationary RC car of mass 2.5kg for 3.0s

a) Calculate the magnitude of the impulse of the force on the car:

b) Calculate the change in speed the impulse produces:

a) I=Ft

I=20\times 3=60Ns

b) Impulse = \Delta p, and \Delta p=mv-mu=m(v-u)

Therefore; 60=2.5(v-0)

v=\cfrac { 60 }{ 2.5 }

v=24\cfrac { m }{ s }

Example 2:

A toy car of mass 2kg is at rest. A force acts on it for 4.0s, increasing its speed to 8\cfrac { m }{ s }

a) Find the impulse the force applies:

I=\Delta p=mv-mu

I=\Delta p=(2\times 8)-(2\times 0)


b) Find the force applied to the car.


16=F\times 4

F=\cfrac { 16 }{ 4 }