Forces on a Box in a Moving Truck

[wyclefchick]

A box is sitting on the floor of a truck. The truck accelerates away from a stoplight. Which statement most accurately describes forces on the box.

A) The box is pushed forward by the force of friction acting in the direction of motion of the truck.

B)The engine of the truck pushes the box backward as it slides across the floor of the truck.

C) The acceleration of ofrce on the box pushes it toward the rear of the truck.

D) The acceleration force on the box is canceled out by the frictional force exerted by the bed of the truck.

E)None of the above

during the test i picked C...is that right?

 

[berkeman]

I don't think C is the correct answer. Think about the situation from the perspective of the box, and carefully re-read the possible answers.

 

[wyclefchick]

well what about in a traffic light and when you hit the gas, the things in your car move backward, and when you hit the break that's when the things move forward

 

[berkeman]

No, for this problem, you need to think of how the box moves (and why) with respect to the Earth, not with respect to the moving reference frame of the car.

When you accelerate away from a light, what is the motion of the box with respect to the ground? Why does it move that way?