Answers to Elementary Mech. Week

[master_q 0]

Answers to Elementary Mechanics Week Trivia

 

 

No one got them all correct. Probably the highest was a below average score (that’s just a estimate - I have not really looked over all the data). Don’t be too shocked because most people score that low on average (even if they taken a physics course - actually that's if they have taken a traditional course {LOL})

 

Anyways let’s look at each problem . . . .

 

Note: I did not care if you had your answer positive if it was technically negative

 

#85: If a smaller starship crashed with a larger starship that was initially at rest, then during this collision what is the force that the larger ship exerts on the smaller one?

 

Answer: C

Why: Remember that quote “Equal and opposite reaction”?

 

#86: A cart is on a track and friction is negligible!!

 

This cart is being pushed with a force of 0.5 Newtons and has a mass of 1 kg.

For all of the following questions something has been changed. You must figure out what effect that will have on its acceleration!

 

Use the following answer key:

A. The acceleration will be greater

B. The acceleration will be less

C. The acceleration will remain the same

D. It is not possible to tell

 

Q1: The towing force is increased to 1 N

Answer: A

Why: It will have a greater force and that will result in a greater acceleration

Q2: Both the mass of the cart and the towing force are doubled

Answer: C

The mass doubles and the force doubles . . . . we have no net gain of force

Q3: The 0.5 N towing force is applied at an downward angle

Answer: B

Why: When we apply it a angle we have to deal with more opposing forces

Q4: The track is inclined

Answer: B

Why: We have to deal with gravity now

Q5: The 0.5 N force is applied to two 500 g cars hooked together

Answer: C

Why: Same total mass and same force

 

#87:

Q1: A block of dry ice resting on a table is given a brief push. A moment later, which of the following forces act on the block?

Answer:

B. a normal force

C. kinetic friction

D. the force of gravity

Why: We are going to get friction. Now must people said gravity, but not the force normal. There has to be something going against gravity or the object would fall down.

 

Q2: Which of the following describes the motion of the block?

Answer:

B. slows down gradually to a stop

Why: Friction!

 

#88:

You are in the back of a friend’s truck when it stalls on a hill. You jump out, get behind the truck and push with all your might (300 N). Still, the truck slowly rolls back down the hill.

The force the truck exerts on you is what?

 

I don’t think anyone go this one correct

Answer: None of the above - It is not possible to tell

Why: We don’t know the angle and we don’t know how much friction. It might be following at a constant rate. (FORCE DOES NOT MAKE SOMETHING MORE IT ACCELERATES IT)

 

#89:

You are in a Starfleet Starship!

 

The ship goes from rest to a very slow speed of 25 miles per second in 10 seconds.

The ship’s velocity is changing at a constant rate.

 

What is its acceleration?

Answer: 2.5 m/s^2

Why: Acceleration is change in velocity over change in time

How far will it travel in 10 seconds?

Answer: 125 mi

Why: The velocity is increasing at a constant rate . . . .

How fast will it be going 3 seconds after it starts?

Answer: 7.5 mi

Why: (basically the same as the answer for 125 mi, but this time we don’t have to figure out the total displacement just sub values into a linear equation)

 

#90:

Q1: Which of the following forces act on the block?

Answer: All of them

A. the towing force

B. a normal force

C. kinetic friction

D. the force of gravity

Q2: Which of the following describes the motion of the block while it is on the table?

The block . . . .

Answer: accelerates constantly (the force will keep accelerating it!)

 

#91: Will A or B have a greater acceleration?

Answer: Everything falls at the same rate!

 

#92: What is the acceleration of “A”?

What is the acceleration of “B”?

Answer: 5 m/s^2

 

#93:

Q1: Determine the acceleration of the elevator

Answer: about 4 m/s^2

Q2: Suppose that a 50 kg woman was standing on a bathroom scale in this elevator car.

What would the scale read? (Don’t make the problem harder then it is - keep the answer in kg)

Answer: 20 kg

Q3: Determine how long it would take for the elevator car (starting from rest) to drop 30 floors (assume each floor is 3 m)?

Answer: 6.7 seconds

 

 

 

Master Q

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