Question

Q1) Answer all Multiple Choice questions.

i) Newton’s 1st law is:

A. PHYSICALLY INDEPENDENT of the other two laws of motion and CANNOT be dispensed with as an axiom of Newtonian physics.

B. PHYSICALLY INDEPENDENT of the other two laws of motion, but nonetheless it CAN be dispensed with as an axiom of Newtonian physics.

C. Actually a SPECIAL CASE of the 2ND LAW. The case when the net force is zero. Therefore, logically we need only two laws of motion. Perhaps for clarity Newton formulated his explicit 1st law and perhaps for the same reason physicists have retained it.

D. Actually a SPECIAL CASE of the 3RD LAW. The case when the net force is zero. Therefore, logically we need only two laws of motion. Perhaps for clarity Newton formulated his explicit 1st law and perhaps for the same reason physicists have retained it.

E. is INCORRECT but is kept in the books for historical reasons.

ii) What is the approximate mass of a woman who weighs 500N? What is gravitational force that Earth exerts on her. After she jumps UPWARD from a diving board, what is her acceleration in the absence of air drag?

A. About 50 kg, 500 N, and 9.8m/s2 downward once she starts moving downward, but ZERO before that.

B. About 50 kg, 50 N, and 9.8m/s2 downward once she starts moving downward, but ZERO before that.

C. About 50 kg, 50 N, and 9.8m/s2 downward at ALL times.

D. About 50 kg, 500N, and 9.8m/s2 downward at ALL times

E. None of these questions can be answered with the given information.

iii) If Newton’s 3rd law is true, why then does anything accelerate at all?

A. The equal and opposite forces DO NOT have to be on the same body.

B. The equal and opposite forces DO have to be on the same body.

C. Nothing moves at all as Parmenides argued in the 5th century BC. Motion is but seeming. Anyway Parmenides seems to have been a pretty smart guy since he’s credited with the spherical Earth theory and the discovery that the Moon shines by reflected light.

D. Acceleration has nothing do with forces.

E. Forces have nothing do with acceleration.

iv) From here on in this course, a key thing to remember (to recite to yourself) when faced with any force problem is that Newton’s 2nd law () is:

A. ALWAYS VALID. And it is a VECTOR equation, and so is always VALID component by component. And is the VECTOR sum of all forces acting on the body of mass m. It is not any particular force. If all the forces sum to zero vectorially, = 0. If you are given the acceleration, then you can often use to solve for an unknown force.

B. ALWAYS VALID. And it is a SCALAR equation. And is the SCALAR sum of all forces acting on the body of mass m. It is not any particular force. If all the forces sum to zero,  = 0. If you are given the acceleration, then you can often use to solve for an unknown force.

C. ONLY VALID when there is a NON-ZERO net force. Because the 2nd law is a VECTOR equation, it is valid (when it is valid) component by component. And is the VECTOR sum of all forces acting on the body of mass m. It is not any particular force. If you are given the acceleration, then you can often use to solve for an unknown force.

D. ALWAYS INVALID.

E. NEVER VALID

v) The force of gravity reaches out across space and pulls on each bit of your body independently of every other bit. We call a force like this a FIELD FORCE or a BODY FORCE. Why don’t you accelerate downward, except when off the ground?

1. The GROUND FORCE reaches out across space and pushes upward on each bit of your body independently of every other bit. The ground force is also a FIELD FORCE

2. The ground exerts a force on the soles of your feet and the soles of your feet on the next layer of your body and the next layer of your body on the next layer of your body and so on until the top of your head. Each layer pushes up with only enough force to balance the gravity force on the mass above. The ground force and the forces exerted by the layers of our bodies areCONTACT FORCES. A CONTACT FORCEacts over a very short range: so short that if the distance between the two objects exerting equal and opposite contact forces on each other is more than microscopic there is no contact force at all.

3. Since you are always off the ground, the question has no answer.

4. Since you are always off the ground, the question is hypothetical and the answer, speculative.

5. In orbit, you don’t accelerate downward, and you are certainly off the ground. So being on the ground may have nothing to do with why you don’t accelerate downward.

vi) Forces can cause accelerations relative to inertial frames or cancel other forces. Another manifestation (which actually follows from their property of causing acceleration) is that they can cause:

A. velocity (without causing acceleration)

B. mass

C. bodies to distort: i.e., flex, compress, stretch, etc

D. bodies to live

E. bodies to rule

vii) A book sits at rest on a table. There action force that follows from Newton’s 3rd law to the gravitational force of the Earth on the book is the:

A. gravitational force of the book on the Earth.

B. normal (i.e., perpendicular upward) force of the table on the book.

C. table friction force on the book.

D. book friction force on the table.

E. book normal force on the table.

Answer 1

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