A truck (mass M) is carrying a box (mass m) in its flatbed, traveling along a straight, level road at speed v, when the driver sees a deer in the road a distance d ahead. The driver slams on the brakes to cause the truck to skid to a stop. The coefficient of kinetic friction between the road and the tires is μt, the coefficient of static friction between the box and the truck bed is μs, and the coefficient of kinetic friction between the box and the truck bed is μk. Draw the free body diagrams of both the box and the truck during the deceleration, and list of all Third Law pairs between the truck and the box. Give Newton's second law equations for the box and the truck, in each direction (4 equations). Does the box slip off the truck? Does the truck hit the deer?
Fnet = ma
Force of friction = μN
The Attempt at a Solution
Now this is a symbolic question (my teacher did not provide numbers at all for it), but I'm stuck with my free body diagrams. I have:
- Gravity pulling down (mg)
- Normal force pushing up from the truck (equal and opposite to mg)
- Some form of friction, but I have no idea. The problem does not specify if it's skidding or staying still. If static, it should be a force pointing in the direction of motion, if kinetic, it should be a force pointing in the opposite direction, yes? But I don't know which to use in my FBD.
- Gravity pulling down (Mg)
- Weight of the box pushing down (mg)
- Normal force up from the road (equal and opposite to Mg + mg)
- Kinetic friction, opposite the direction of motion (μt)
- I'm not sure if the friction from the truck on the box is also applying a force on the truck, or what that force might even be.