# Q1) Answer all Multiple Choice questions. i) Newton’s 1st law is: A. PHYSICALLY INDEPENDENT of the…

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?

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

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 are

CONTACT FORCES. A CONTACT FORCE

acts 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.

Since you are always off the ground, the question has no

answer.

Since you are always off the ground, the question is

hypothetical and the answer, speculative.

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.

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