Q: A 2 kg object is suspended by a rope and is accelerating upward at $$3\ \mathrm{m/s^2$}. $$What is the tension in the rope?

$$T = m(a + g) = 2\ \mathrm{kg} \times (3 + 9.8)\ \mathrm{m/s^2$} = 25.6\ \mathrm{N}$$

Q: A 4 kg block is connected by a string over a frictionless pulley to a 7 kg block hanging vertically. If the coefficient of kinetic friction between the 4 kg block and the surface is $$\mu_k = 0.3$$, what is the acceleration of the system? (Use $$g = 9.8\ \mathrm{m/s^2$})$$

$$a = \frac{m_2g - \mu_k m_1$ g}{m_1$ + m_2$} = \frac{7 \times 9.8 - 0.3 \times 4 \times 9.8}{4 + 7} = \frac{68.6 - 11.76}{11} = 5.16\ \mathrm{m/s^2$}$$

Question 1

Which of the following best describes Newton's First Law of Motion?

Accepted Answer

An object will remain at rest or move with constant velocity unless acted upon by a net external force.

Question 2

A 5 kg box is pulled across a frictionless surface by a horizontal force of 20 N. What is the acceleration of the box?

Accepted Answer

$$a = \frac{F}{m} = \frac{20\ \mathrm{N}}{5\ \mathrm{kg}} = 4\ \mathrm{m/s^2$}$$

Question 3

Which of the following is NOT a fundamental force of nature?

Accepted Answer

Frictional force

Question 4

Two forces, $$F_1 = 3$$\ \mathrm{N}$$ and F_2$ = 4\ \mathrm{N}$$, act perpendicularly on an object. What is the magnitude of the resultant force?

Accepted Answer

$$F = \sqrt{F_1$^2 + F_2$^2} = \sqrt{3^2$ + 4^2$} = 5\ \mathrm{N}$$

Question 5

A 70 kg astronaut pushes against a 140 kg satellite in space. If the astronaut moves away at $$0.5\ \mathrm{m/s}$$, what is the velocity of the satellite after the push?

Accepted Answer

$$v = -0.25\ \mathrm{m/s}$$

Question 6

Which statement about the normal force is correct for an object of mass $$m$$ resting on a horizontal surface with no other vertical forces?

Accepted Answer

$$n = mg$$

Question 7

A 2 kg object is suspended by a rope and is accelerating upward at $$3\ \mathrm{m/s^2$}. $$What is the tension in the rope?

Accepted Answer

$$T = m(a + g) = 2\ \mathrm{kg} 	imes (3 + 9.8)\ \mathrm{m/s^2$} = 25.6\ \mathrm{N}$$

Question 8

Which of the following is an example of a field force?

Accepted Answer

The gravitational attraction between the Earth and the Moon

Question 9

A 10 kg box is at rest on a horizontal surface. A horizontal force of 30 N is applied, but the box does not move. What can you conclude about the frictional force?

Accepted Answer

The frictional force is 30 N, acting opposite to the applied force.

Question 10

Which of the following best illustrates Newton's Third Law of Motion?

Accepted Answer

A swimmer pushes water backward, and the water pushes the swimmer forward.

Question 11

A 350 kg airboat experiences a net horizontal force of 770 N. What is its acceleration?

Accepted Answer

$$a = \frac{770\ \mathrm{N}}{350\ \mathrm{kg}} = 2.2\ \mathrm{m/s^2$}$$

Question 12

Which of the following is the correct SI unit for force?

Accepted Answer

$$1\ \mathrm{N} = 1\ \mathrm{kg}\,\mathrm{m/s^2$}$$

Question 13

A 4 kg block is connected by a string over a frictionless pulley to a 7 kg block hanging vertically. If the coefficient of kinetic friction between the 4 kg block and the surface is $$\mu_k = 0.3$$, what is the acceleration of the system? (Use $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$a = \frac{m_2g - \mu_k m_1$ g}{m_1$ + m_2$} = \frac{7 	imes 9.8 - 0.3 	imes 4 	imes 9.8}{4 + 7} = \frac{68.6 - 11.76}{11} = 5.16\ \mathrm{m/s^2$}$$

Question 14

Which of the following is a correct statement about mass and inertia?

Accepted Answer

The greater the mass of an object, the greater its resistance to changes in motion.

Question 15

A 1 kg object is hanging at rest from a rope. What is the tension in the rope?

Accepted Answer

$$T = mg = 1\ \mathrm{kg} 	imes 9.8\ \mathrm{m/s^2$} = 9.8\ \mathrm{N}$$

Question 16

Which of the following is the correct vector equation for Newton's Second Law?

Accepted Answer

$$\sum \vec{F} = m \vec{a}$$

Question 17

A 10 kg box is on a frictionless incline of $$30^\circ. $$What is the normal force acting on the box?

Accepted Answer

$$n = mg \cos 	heta = 10 	imes 9.8 	imes \cos 30^\circ = 84.9\ \mathrm{N}$$

Question 18

Which of the following is NOT a property of force?

Accepted Answer

Force is a scalar quantity.

Question 19

A 1 lb mass is attracted to the Earth with a force of approximately how many Newtons?

Accepted Answer

$$1\ \mathrm{lb} \approx 4.45\ \mathrm{N}$$

Dynamics: Newton's Laws of Motion – Study Notes

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