Question

i. testing concepts
directions: for each of the following, write the letter of the term or phrase that best completes each statement or answers each question.

1. the upward force exerted on an object falling through air is _.

a. terminal velocity b. momentum c. air resistance d. weightless

1. when an object moves in a circular path, the unbalanced force causing the object to change direction is _.

a. terminal velocity b. momentum c. centripetal force d. friction

1. the statement “to every reaction there is an equal and opposite reaction” is _.

a. the law of conservation of momentum b. newton’s first law of motion c. newton’s second law of motion d. newton’s third law of motion

1. when two objects cannot slide past each other it has _.

a. sliding friction b. rolling friction c. inertia d. static friction

1. when two objects collide, their momentum after the collision is explained by _.

a. newton’s first law of motion b. newton’s second law of motion c. newton’s third law of motion d. the conservation of momentum

1. a feather will fall through the air more slowly than a brick because of _.

a. gravity b. air resistance c. terminal velocity d. momentum

1. the amount of gravitational force between objects depends on their _.

a. frictional forces b. speed and direction c. inertia d. masses and the distances between them
directions: do the following calculations. show your work in the spaces provided.

1. what is the force of an object with a mass of 12 kg and an acceleration of 4 m/s²?
2. calculate the acceleration of a 25 - kg object that is moved with a force of 300 n.
3. explain how your weight is different on earth than it would on the moon.

Explanation:

1.

Air resistance is the upward force on a falling object. Terminal velocity is the constant speed when air resistance equals weight. Momentum is mass times velocity. Weightless is a state. So the answer is c.

2.

Centripetal force causes circular - path direction change. Terminal velocity is for falling. Momentum is mass × velocity. Friction opposes sliding. So the answer is c.

3.

Newton's third law: every action has an equal and opposite reaction. Conservation of momentum is about momentum before and after. Newton's first law is about inertia. Second law is \(F = ma\). So the answer is d.

4.

Static friction is when objects don't slide. Sliding friction is when they do. Rolling friction is for rolling. Inertia is resistance to motion change. So the answer is d.

5.

Conservation of momentum explains post - collision momentum. Newton's first law is inertia. Second law is \(F = ma\). Third law is action - reaction. So the answer is d.

6.

Air resistance slows the feather more. Gravity acts on both. Terminal velocity depends on air resistance. Momentum is mass × velocity. So the answer is b.

7.

Gravitational force \(F=\frac{Gm_1m_2}{r^{2}}\), depends on masses (\(m_1,m_2\)) and distance (\(r\)). Frictional forces are different. Speed/direction not in formula. Inertia is mass property. So the answer is d.

8.

Using Newton's second law \(F = ma\).
Given \(m = 12\space kg\), \(a=4\space m/s^{2}\).
\(F=(12\space kg)\times(4\space m/s^{2})\)
\(F = 48\space N\)

9.

From \(F = ma\), we can solve for \(a=\frac{F}{m}\).
Given \(F = 300\space N\), \(m = 25\space kg\).
\(a=\frac{300\space N}{25\space kg}\)
\(a = 12\space m/s^{2}\)

10.

Weight \(W=mg\), where \(g\) is the acceleration due to gravity.
On Earth \(g_{Earth}\approx9.8\space m/s^{2}\), on the Moon \(g_{Moon}\approx1.6\space m/s^{2}\).
Since mass \(m\) (amount of matter) is constant, \(W_{Earth}=m\times g_{Earth}\) and \(W_{Moon}=m\times g_{Moon}\).
Because \(g_{Earth}>g_{Moon}\), \(W_{Earth}>W_{Moon}\)

Answer:

1. c. air resistance
2. c. centripetal force
3. d. Newton’s third law of motion
4. d. static friction
5. d. the conservation of momentum
6. b. air resistance
7. d. masses and the distances between them
8. \(48\space N\)
9. \(12\space m/s^{2}\)
10. Weight \(W = mg\). Mass \(m\) is constant. \(g_{Earth}\approx9.8\space m/s^{2}\), \(g_{Moon}\approx1.6\space m/s^{2}\). Since \(g_{Earth}>g_{Moon}\), \(W_{Earth}>W_{Moon}\)