Question

modified true/false circle true or false first. if false, change the incorrect word or phrase. 2 marks - k/u

1. an object with a zero net external force must remain at rest

true false

1. safety measures in cars such as airbags and seatbelts are directly related to newtons second law.

true false
multiple choice circle the choice that best completes the statement or answers the question. 8 marks - k/u

1. a 74 kg skier experiences a net force of 185 n downhill. what is the magnitude of his acceleration?

2.5 m/s² b. 13000 m/s² c. 14000 m/s² d. 9.8 m/s² e. 0.39 m/s²

1. what is the magnitude of the net force of a 10. kg ball falling through the air (ignore air resistance)?

9.8 n b. 98 n c. 98 m/s² d. 9.8 m/s² e. 0 m/s²

1. a 5.0 kg object is moving at a constant velocity on a desk where friction is present. if the person applies a force of 55 n right on the block, what would the force of friction be?

280 n w b. 55 n e c. 0 n w d. 55 n w e. none of above

1. which of the following scenarios must be true about a non - zero net external force?
2. the applied force must be zero b. the acceleration of the object is non - zero

c. the object is moving at a constant velocity d. the force of friction must be zero
e. the direction of the applied force and the force of friction is the same

1. which statement is true for two balls with the same mass dropped off of a building?
2. the force of gravity is the same for the balls, and acceleration due to gravity is the same

b. the force of gravity is the same for the balls, but acceleration due to gravity is different
c. the force of gravity is different for the balls, but acceleration due to gravity is the same
d. the force of gravity is different for the balls, and acceleration due to gravity is different

1. which statement best describes a tension force?
2. an internal force of an object

b. a force that resists change in motion or attempted motion of an object
c. a perpendicular force exerted by a surface
d. a force in a string or rope when pulled
e. a force opposing gravity

1. you are pushing a mass m with a force f. if you reduce the mass by a half (1/2 m), what effect will it have on the acceleration of the object?
2. double b. triple c. half d. no effect e. undetermined

Explanation:

1. Modified True/False

Question 1

• Step1: Recall Newton's First Law

Newton's First Law states that an object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an un - balanced force. An object with a zero net external force can be at rest or in uniform motion.

• Step2: Correct the statement

The incorrect phrase is “must remain at rest”. It should be “remains at rest or in uniform motion”.

Question 2

• Step1: Recall Newton's Laws related to safety measures

Safety measures like airbags and seatbelts are related to Newton's First Law (inertia). When a car suddenly stops, the person in the car has a tendency to keep moving due to inertia. Airbags and seatbelts counteract this tendency.

• Step2: Correct the statement

The incorrect phrase is “Newton's Second Law”. It should be “Newton's First Law”.

2. Multiple - Choice

Question 3

• Step1: Use Newton's Second Law \(F = ma\)

We know that \(a=\frac{F}{m}\), where \(F = 185N\) and \(m = 74kg\).

• Step2: Calculate the acceleration

\(a=\frac{185}{74}=2.5m/s^{2}\)

Question 4

• Step1: Use \(F = ma\) for free - fall

For an object in free - fall (ignoring air resistance), \(a = g=9.8m/s^{2}\) and \(m = 10kg\). Using \(F=ma\), we substitute the values.

• Step2: Calculate the net force

\(F=(10)(9.8)=98N\)

Question 5

• Step1: Analyze the forces for constant velocity

When an object is moving at a constant velocity, the net force is zero. If the applied force \(F_{applied}=55N[Right]\), then the frictional force \(F_f\) must be equal in magnitude and opposite in direction.

• Step2: Determine the frictional force

\(F_f = 55N[Left]\) (assuming right is positive and left is negative in a one - dimensional coordinate system related to the motion on the desk)

Question 6

• Step1: Recall Newton's Second Law \(F = ma\)

If \(F
eq0\), then from \(F = ma\), \(a=\frac{F}{m}\). Since \(m>0\) (mass of an object is non - zero), \(a
eq0\)

Question 7

• Step1: Use \(F = mg\) and \(a = g\) for free - fall

The force of gravity \(F = mg\). Since \(m_1=m_2\) (same mass) and \(g\) (acceleration due to gravity) is a constant near the Earth's surface (\(g = 9.8m/s^{2}\)), \(F_1=F_2\) and \(a_1 = a_2=g\)

Question 8

• Step1: Define tension force

Tension force is the force exerted by a string or rope when it is pulled.

• Step2: Eliminate other options
• Option a: Tension is an external force (e.g., when you pull a rope attached to a block).
• Option b: This is the definition of frictional force.
• Option c: This is the definition of normal force.
• Option e: Tension is not specifically a force opposing gravity.

Question 9

• Step1: Use \(F = ma\) and consider the change in mass

Initially, \(a_1=\frac{F}{m}\). When \(m_2=\frac{1}{2}m\), then \(a_2=\frac{F}{\frac{1}{2}m}=2\frac{F}{m}=2a_1\)

Answer:

1.

• Question 1: False; remains at rest or in uniform motion
• Question 2: False; Newton's First Law

2.

• Question 3: a. \(2.5m/s^{2}\)
• Question 4: b. \(98N\)
• Question 5: d. \(55N[W]\)
• Question 6: b. the acceleration of the object is non - zero
• Question 7: a. the force of gravity is the same for the balls, and acceleration due to gravity is the same
• Question 8: d. a force in a string or rope when pulled
• Question 9: a. Double