Question

Question: A large crate of mass m is place on the flatbed of a truck but not tied down. As the truck accelerates forward with acceleration a, the crate remains at rest relative to the truck. What force causes the crate to accelerate? (a) the normal force (b) the gravitational force (c) the friction force (d) the ma force exerted by the crate (e) No force is required.

Short answer

The correct option is (c): the friction force.

Step-by-step solution

Write the given data from the question

he mass of the crate is $\mathrm{m}$.

The acceleration of the truck is $\mathrm{a}$.

Determine the force that causes the crate to accelerate

When the surfaces of two bodies come in contact and slide over each other, a force is produced between them; this is known as the frictional force.

The equation to calculate the frictional force is as follows.

${\mathrm{f}}_{\mathrm{k}}={\mathrm{\mu }}_{\mathrm{k}}\mathrm{n}$

Here, ${\mathrm{\mu }}_{\mathrm{k}}$is the coefficient of the kinetic friction, and is the normal force.

The force acting between the truck flatbed and crate is the frictional force, which accelerates the crate.

Hence, the friction force causes the crate to accelerate.