Forces and Free-Body Diagrams - AP Physics 1

1. Calculate the gravitational force on a 10 kg mass on Earth's surface.

   $F = 98 \text{ N}$. Using $W = mg = 10 \times 9.8 = 98 \text{ N}$.

2. What is the effect on acceleration if net force is doubled?

   Acceleration doubles. From $F = ma$; doubling force doubles acceleration for constant mass.

3. State Newton's First Law of Motion.

   An object in motion stays in motion unless acted on by a net external force. Also called the law of inertia; objects resist changes in motion.

4. What is the effect on net force if two equal forces act in opposite directions?

   Net force is 0 N. Equal and opposite forces cancel completely.

5. What is the unit of gravitational constant $G$?

   $\text{N m}^2 \text{kg}^{-2}$. Units derived from $F = G \frac{m_1 m_2}{r^2}$ dimensional analysis.

6. What is the direction of the net force on an object moving in a circle?

   Towards the center of the circle. Centripetal force always points toward the center of circular motion.

7. What is the formula for kinetic frictional force?

   $f_k = \text{μ}_k N$. Kinetic friction equals coefficient times normal force.

8. Find the value of the normal force on an inclined plane.

   $N = mg \, \cos \theta$. Normal force is weight component perpendicular to inclined plane.

9. Identify the force that opposes the relative motion of two surfaces.

   Frictional force. Kinetic and static friction resist sliding between contact surfaces.

10. What is the resultant force of 10 N and 15 N acting in the same direction?

    25 N in the direction of both forces. Add forces in same direction: $10 \text{ N} + 15 \text{ N} = 25 \text{ N}$.

11. What is the term for the force causing an object to move in a circle?

    Centripetal force. The net inward force required for circular motion.

12. Calculate the net force on an object with 8 N right and 3 N left.

    5 N to the right. Net force: $8 \text{ N} - 3 \text{ N} = 5 \text{ N}$ rightward.

13. State Newton's Third Law of Motion.

    For every action, there is an equal and opposite reaction. Forces always occur in equal and opposite pairs between objects.

14. Which force is responsible for an object sliding down an inclined plane?

    Component of gravitational force parallel to the plane. Component $mg \sin \theta$ acts parallel to inclined surface.

15. Calculate the friction force for $μ_k = 0.3$ and $N = 50 \text{ N}$.

    $f_k = 15 \text{ N}$. Using $f_k = \text{μ}_k N = 0.3 \times 50 = 15 \text{ N}$.

16. Which force always acts opposite to the direction of motion?

    Frictional force. Friction always opposes relative motion between surfaces in contact.

17. How does increasing mass affect gravitational force?

    Gravitational force increases. Force is proportional to both masses in gravitational equation.

18. Find the normal force on a 10 kg object on a flat surface.

    $N = 98 \text{ N}$. Normal force equals weight on horizontal surface: $N = mg$.

19. What is the formula for gravitational force between two masses?

    $F = G \frac{m_1 m_2}{r^2}$. Newton's law of universal gravitation relates force to masses and distance squared.

20. What is the formula for centripetal force?

    $F_c = \frac{mv^2}{r}$. Force needed to maintain circular motion at constant speed.

21. Choose the correct formula for tension in a rope with mass $m$ accelerating upward.

    $T = m(g + a)$. Tension must overcome weight plus provide upward acceleration force.

22. Identify the force that balances the weight of a stationary object on a table.

    Normal force. Normal force provides upward support equal to object's weight.

23. Which force acts on a hanging object in a stationary elevator?

    Tension equal to weight. Tension balances weight when elevator moves at constant velocity.

24. State the formula for Newton's Second Law of Motion.

    $F = ma$. Force equals mass times acceleration; fundamental dynamics equation.

25. What is the formula for calculating weight?

    $W = mg$. Weight equals mass times gravitational acceleration ($g = 9.8 \text{ m/s}^2$).

26. What is the formula for static frictional force?

    $f_s \, \leq \, \text{μ}_s N$. Static friction can vary up to maximum value $\text{μ}_s N$.

27. Identify the main force that acts at a distance without contact.

    Gravitational force. Gravity acts between all masses without physical contact.

28. What happens to friction if the normal force is doubled?

    Friction doubles. Friction is directly proportional to normal force.

29. Determine the tension in a rope holding a 5 kg mass at rest.

    $T = 49 \text{ N}$. At rest, tension equals weight: $T = mg = 5 \times 9.8 = 49 \text{ N}$.

30. What is the unit of force in the International System of Units?

    Newton (N). Named after Isaac Newton; equivalent to $\text{kg} \cdot \text{m/s}^2$.

31. Identify the force exerted by a surface perpendicular to the object.

    Normal force. Normal force acts perpendicular to contact surfaces, preventing penetration.

32. What is the formula for net force on an inclined plane?

    $F_{\text{net}} = mg \, \sin \theta - f$. Gravity component minus friction determines net acceleration down plane.

33. State the relationship between mass and weight.

    Weight is mass times gravitational acceleration. Mass is intrinsic; weight depends on gravitational field strength.

34. Which force acts on a satellite orbiting Earth?

    Gravitational force. Earth's gravity provides centripetal force for orbital motion.

35. What is the formula for restoring force in a spring?

    $F = -kx$. Hooke's law; negative sign indicates force opposes displacement.

36. Identify the net force on an object in equilibrium.

    Net force is 0 N. In equilibrium, all forces cancel out, resulting in zero net force.

37. Identify the force that acts between two charged objects.

    Electrostatic force. Coulomb force between charges; can be attractive or repulsive.

38. Find the net force if an object has forces of 5 N and 3 N in opposite directions.

    Net force is 2 N in the direction of the larger force. Subtract opposing forces: $5 \text{ N} - 3 \text{ N} = 2 \text{ N}$.

39. What is the relationship between acceleration and net force?

    Directly proportional. From Newton's second law: $a = \frac{F}{m}$.

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