**1. **

According to the law of conservation of momentum, the momentum of an **isolated **system is **constant**.** **

For a head-on collision, we express the equation of conservation of momentum as:

$\overline{){{\mathbf{m}}}_{{\mathbf{1}}}{{\mathbf{v}}}_{{\mathbf{01}}}{\mathbf{=}}{{\mathbf{m}}}_{{\mathbf{1}}}{{\mathbf{v}}}_{\mathbf{f}\mathbf{1}}{\mathbf{+}}{{\mathbf{m}}}_{{\mathbf{2}}}{{\mathbf{v}}}_{\mathbf{f}\mathbf{2}}}$

In this case, let's take subscript **t **to represent the truck and **c** the car.

1. A truck going 15 km/h has a head-on collision with a small car going 30 km/h. Which statement best describes the situation?

A. The truck has the greater change of momentum because it has the greatest mass.

B. The car has the greater change of momentum because it has the greater speed.

C. Neither the car nor the truck changes its momentum in the collision because momentum is conserved.

D. They both have the same change in magnitude of momentum because momentum is conserved.

E. None of the above is necessarily true.

2. A heavy sack of sand is dropped from the bridge onto the boat. The speed of the boat

A. increases.

B. decreases.

C. does not change.

D. Without knowing the mass of the boat and the sand, we can't tell.

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