Q: A person stands on a scale in an elevator that is accelerating downward at $$2 \ \mathrm{m/s^2$}. If $$the person's mass is $$70 kg$$, what is the apparent weight shown on the scale?

$$70 \times (9.8 - 2) = 546 N$$

Q: A 1.5 kg mass hangs from a vertical spring. The spring stretches from its natural length of $$0.30 m to$$ $$0.34 m. $$What is the spring constant $$k$$?

$$k = \dfrac{1.5 \times 9.8}{0.04} N/m$$

Question 1

Which of the following statements best describes Newton's third law of motion?

Accepted Answer

For every action, there is an equal and opposite reaction, and these forces act on different objects.

Question 2

A 2 kg object is at rest on a horizontal table. The gravitational force acting on the object is $$w = mg. $$What is the magnitude of the normal force exerted by the table on the object?

Accepted Answer

$$19.6 N$$

Question 3

Two blocks, with masses $$m_1 = 2.3$ kg and m_2$ = 1.2 kg$$, are in contact on a frictionless table. A horizontal force $$F = 3.2 N is $$applied to block 1. What is the acceleration of the system?

Accepted Answer

$$a = \dfrac{3.2}{2.3 + 1.2} \ \mathrm{m/s^2$}$$

Question 4

Which of the following is NOT a correct statement about Newton's law of universal gravitation?

Accepted Answer

The gravitational force between two objects can be repulsive if one mass is negative.

Question 5

A person stands on a scale in an elevator that is accelerating downward at $$2 \ \mathrm{m/s^2$}. If $$the person's mass is $$70 kg$$, what is the apparent weight shown on the scale?

Accepted Answer

$$70 	imes (9.8 - 2) = 546 N$$

Question 6

Which of the following pairs of forces are Newton's third law action-reaction pairs?

Accepted Answer

The force of the Earth pulling on a falling apple and the force of the apple pulling on the Earth.

Question 7

A block is pulled by a rope with a slowly increasing tension $$T on a $$table with coefficient of static friction $$\mu_s. $$The block remains stationary. Which statement is always true?

Accepted Answer

The friction force is always equal to the applied tension $$T.$$

Question 8

A 1.5 kg mass hangs from a vertical spring. The spring stretches from its natural length of $$0.30 m to$$ $$0.34 m. $$What is the spring constant $$k$$?

Accepted Answer

$$k = \dfrac{1.5 	imes 9.8}{0.04} N/m$$

Question 9

A block of mass $$m is $$being lifted at constant speed by a rope. What is the tension $$T in $$the rope?

Accepted Answer

$$T = mg$$

Question 10

A 0.5 kg ball is dropped from rest. Neglecting air resistance, what is the net force acting on the ball during its fall?

Accepted Answer

$$4.9 N$

Question 11

A 3 kg block is pulled across a horizontal surface with a constant velocity. The coefficient of kinetic friction is $$\mu_k = 0.2. $$What is the magnitude of the friction force?

Accepted Answer

$$0.2 	imes 29.4 = 5.88 N$$

Question 12

Which of the following best describes the direction of the friction force acting on a block at rest on an inclined plane?

Accepted Answer

Up the incline, opposing the component of gravity down the incline.

Question 13

A 0.1 kg sphere falls through air with a drag force $$D = \frac{1}{2} C_D \rho A v^2$. If C_D = 1.1$, A = 0.01$ m^2$, $$\rho = 1.2$$ kg/m^3$, and g = 9.8$ m/s^2$, what is the terminal speed v_t$?

Accepted Answer

$$v_t = \sqrt{\dfrac{2mg}{C_D \rho A}}$$

Question 14

Which of the following statements about action-reaction pairs is correct?

Accepted Answer

They act on different objects and never cancel each other.

Question 15

A block is at rest on a table. Which of the following forces form a Newton's third law pair?

Accepted Answer

The force of the block on the table and the force of the table on the block.

Question 16

A 0.5 kg object is attached to a spring with spring constant $$k = 200 N/m. If $$the spring is compressed by 0.02 m, what is the magnitude of the spring force?

Accepted Answer

$$F = 200 	imes 0.02 N$$

Question 17

A block is pulled by a rope on a table with kinetic friction. Once the block starts moving, which statement is correct?

Accepted Answer

The friction force is always equal to $$\mu_k N.$$

Question 18

A 1 kg object is moving through a fluid with viscosity $$\eta. At $$low Reynolds number, what is the drag force acting on the object if its radius is $$r$$ and speed is $$v$$?

Accepted Answer

$$D = 6 \pi \eta r v$$

Question 19

Which of the following best describes the equilibrium condition for a system in two dimensions?

Accepted Answer

$$\sum F_x = m a_x = 0$$ and $$\sum F_y = m a_y = 0$$

Newton's Laws, Gravity, and Equilibrium: Study Notes

Study Guide - Practice Questions

Study Guide - Flashcards