Two masses one woman one acceleration

[laurenwings5]

1. A small car of mass 708 kg is parked behind
a small truck of mass 1797 kg on a level road.
The brakes of both the car and the truck are
off so that they are free to roll with negligible
friction. A 81 kg woman sitting on the tailgate
of the truck shoves the car away by exerting
a constant force on the car with her feet. The
car accelerates at 1.3 m/s2.
What is the acceleration of the truck?
Answer in units of m/s2.


2. Using F = ma, we know that she exerts a force of 920.4 N. But what would the acceleration of the truck be? I don't understand how to solve that problem.

 

[ehild]

The car, women and truck are a system subject to inner forces only. The centre of mass stays in rest.

ehild

 

[laurenwings5]

so that means that the acceleration of the truck is 0 m/s^2?

 

[The legend]

^ yes , i think ..

 

[ehild]

so that means that the acceleration of the truck is 0 m/s^2?

No. The common centre of mass of the whole system stays in rest, as there are no external forces. The women exerts force on the truck, the truck exerts force on the women+truck.

ehild

 

[The legend]

ok, i got it!