Homework Help: Simple multiple choice questions

1. May 9, 2012

yesiammanu

I'm taking a final tomorrow and was just wondering if someone could confirm that these (most missed) multiple choice questions on the previous exams are answered correctly. Again, this isn't homework, they are old test questions

The "Principle of Equivalence" states that __________ and ___________ are experimentally indistinguishable!
a. mass, energy b. velocity, speed c. force, mass d. particles, waves e. None of the above!
A: e - principle of equivalence states that acceleration due to gravity and acceleration due to frame of reference are experimentally indistinguishable

If you reverse the order of operation for two vectors A and B, which of the following results is (are) affected?
a. A + B b. A - B c. the dot product d. the cross product e. Both b and d are affected!
A: e - crossproduct and subtraction both rely on position in the matrix

The next three questions refer to a 10.0 kg mass which is moving in the x direction as given by, x(t) = 10.0 t2 + 5.00 t where x is measured in meters and t is measured in seconds starting at t = 0
15. Which of the following is a constant?
a. velocity b. position c. speed d. net external force e. None of the above!
A: d - force is constant because there is no jerk in the equation

The result of the following operation involving five non-zero vectors is, [(A x B) x C](E dot F)
a. a vector b. a scalar c. You can't tell from the information given!
A: I have no idea, actually. I'd assume that it would be a vector since the first 3 would go in the ij direction

An ideal Hooke's law spring is stretched from zero to 10.0 cm and 1.00 J of work is done by the external force stretching the spring. If the same spring is stretched from zero to 20.0 cm, how much work did the external force do?
a. still 1.00 J b. 2.00 J c. 4.00 J d. 8.00 J e. None of the above are even close!
A: Hookes law - 1/2 k x2, so it would do 4x as much work, 4 joules.

True or False: No matter how hard you push on a body, if the body doesn't move then your force has not applied any impulse to it!
a. True b. False c. I don't have a clue!
A: Impulse is the change in momentum, and momentum = m * v, so since the velocity is still 0, it would be True

In any collision, what quantity (or quantities) MUST be conserved?
a. total energy b. linear momentum c. potential energy d. kinetic energy e. both "a" and "b" above
A: e - Potential energy and kinetic energy is in general form, mechanical energy which is not conserved by elastic collisions

A typical passenger car traveling at 30.0 MPH can stop on dry pavement in a minimum distance of about 20.0 m. At 90.0 MPH, under the same conditions, the same vehicle should stop in a distance of about ______ meters.
a. 40.0 b. 60.0 c. 80.0 d. 100. e. 180
A: kinetic energy is 1/2 m*v2, so when trippling speed, you increase distance factor by 9. Therefore, it is e, 180m

In a collision, a large SUV and a Mini Cooper hit head-on. Which experiences the greatest magnitude impulse during the collision?
a. the Mini b. the SUV c. both impulses are equal d. None of the above is correct!
A: Since p = mv, the SUV will have more mass than a mini cooper and therefore lose more momentum when they strike head on (assuming they stop completely), so b is correct

Thanks for the help

Last edited: May 9, 2012
2. May 9, 2012

tiny-tim

hi yesiammanu!

they're all fine down to and including the hooke's law question (after that, i got bored)

the missing one …
… is easy if you do it in bits

the () is a dot product, so it's a … ?
the [] is a cross product of a cross product, so it's a … ?
and can you combine those two?

3. May 9, 2012

yesiammanu

The [] is a crossproduct so it goes in the xysintheta direction towards the z axis due to the right hand rule, which implies a vector
The dot product creates a scalar, and when a scalar is multiplied by a vector, you end with a vector (so that speed * velocity = velocity). So the answer is a vector. Thanks!

For this one:
True or False: No matter how hard you push on a body, if the body doesn't move then your force has not applied any impulse to it!
a. True b. False c. I don't have a clue!
A: Impulse is the change in momentum, and momentum = m * v, so since the velocity is still 0, it would be True

Apparently I got this wrong, but I'm not really sure why.

4. May 9, 2012

tiny-tim

definitions …

work = force times distance … zero!

impulse = force times time … non-zero!

(there's an equal and opposite impulse from whatever is restraining the body, that's why it doesn't move! )

good luck tomorrow!