【单选题】A large crate of mass m is placed on the back of a truck but not tied down. As the truck accelerates forward with an acceleration a, the crate remains at rest relative to the truck. What force causes ...
A.
the normal force
B.
the force of gravity
C.
the force of friction between the crate and the floor of the truck
【单选题】A large crate of mass m is placed on the back of a truck but not tied down. As the truck accelerates forward with an acceleration a, the crate remains at rest relative to the truck. What force causes ...
A.
the normal force
B.
the force of gravity
C.
the force of friction between the crate and the floor of the truck