emergency physics sl help!

[ArielYao]

please provide explanations to the questions, if you know the answer. I have a test tomorrow and still have some unsolved problems. Thanks a lot !!!! =)

[khimberleigh]

For question #8:

The highest resultant force that could occur is 18 because 5+6+7=18 (that would occur if all the forces were acting in the exact same direction)

Therefore, 19 is impossible

#6:

change in momentum equals Pfinal-Pinitial

remember P=mv, now m will be the same for both Pf and Pi but the velocities will be opposite signs because the ball switches direction

therefore change in momentum = mv - -mv which is the same as mv+mv or 2mv

#5

once the ball leaves the throwers hand the only force acting on it is gravity therefore it will be accelerating down (even though it is travelling up), therefore the velocity must be decreasing initially until it stops when it reaches maximum height and continues to accelerate down. Unless the question specifically states that there is air resistance you can assume it is negligible. As the only force again is gravity the object's acceleration is constant. Therefore, the velocity graph must be a straight line and not curved.

#4

I'm not exactly sure but I would probably say C because initially the first ball will be travelling faster because it had been accelerating for longer but when the balls both reach terminal speed (which will occur because there is air resistance) the distance between the balls will be constant again.

I hope that kind of makes sense

Edited January 1, 2014 by khimberleigh

[ctrls]

8) The direction of the forces isn't stated, so they could be in any configuration. If all forces could be pushing the object in the same direction (so they all add up), but they could all be pushing in opposite directions, so they cancel out and give a net force of 0. As a result, you get a range of possible magnitudes the net force can be, depending on the arrangement of the forces.

The maximum force you can get is then they all are in the same direction, so they add up. In this case 5+6+7=18N, which is the maximum net force that could act on the object. Because 19N exceeds this maximum, it cannot be the resultant force, given any configuration of the three forces.

On a side-note, 4 is a bit ambiguous in my opinion. Strictly speaking the distance increases as the first ball accelerates, then it decreases while it decelerates, then stays constant as they both reach terminal velocity. C is the right answer, but it's a bit confusing since they don't mention the middle step.

Edited January 1, 2014 by ctrls

[ArielYao]

Thank you guys very much for the answers!

some extra concerns :

could you please provide explanations for these questions as well

[Fiz]

4) You have The Force "F" with an angle. Now, since there is an angle "theta", then the force to the right is equal to "Fcos(theta)". and since its at constant Velocity, then Frictional Force = Fcos(theta)

Now, when looking at the vertical axis, we can see that there are 3 types of forces

1- Gravitational Force [Mg] (downwards)

2- Normal Force [R] (upwards)

3- Fsin(theta) (upwards)

Now, since the object is in vertical equilibrium, then:

Mg = Fsin(theta) + R

So, we know that Friction is always against the direction of motion, so it must be dragging it to the right.

The force to the right is at an angle, so it must be drawn at an angle.

We know that since Mg is equal to both Fsin(theta) and R, then R (normal force) can never be equal to Weight, so it MUST be shorter.

Thus, we can conclude that only D would be the correct answer

(Correct me if i am wrong)

[Fiz]

Now, question 8 is pretty straight forward.

You have a pendulum, that is moving. If it was stationary, according to newton's first law of motion, choice D would be the correct answer. (Remember objects in motion are not treated as objects with constant acceleration).

Here is a picture attachment that might be able to help you.

The tension of the sting here is equal to = mg + centripetal force. So Tension is surely greater than Mg! Hope this helps!

Good luck with your physics!

-Fiz

[ArielYao]

thanks for all your active answers! but I don't know for question 8, how is the resultant force of “0” possible ? Please explain in detail.

[Nero]

for Q8, Answer d is wrong because the mass is not motionless

c is right because when the mass falls and there is an additional centripetal force added the original mass

if motionless resultant force is 0 since the tension = mg

Edited January 1, 2014 by Nero

[ArielYao]

Now, question 8 is pretty straight forward.

You have a pendulum, that is moving. If it was stationary, according to newton's first law of motion, choice D would be the correct answer. (Remember objects in motion are not treated as objects with constant acceleration).

Here is a picture attachment that might be able to help you.

The tension of the sting here is equal to = mg + centripetal force. So Tension is surely greater than Mg! Hope this helps!

Good luck with your physics!

-Fiz

thank you! =)i don't quite get your graph, but i understand the question now. at my level, i'd treat the problem as “ there's a potential of movement ”, so the pendulum is not at translational equilibrium.

[ArielYao]

a new quite confusing problem

[Nero]

ariel what subjects do you have other than physics?

[Fiz]

Well, inorder to understand question 8 you must have taken the Centripetal force and centripetal acceleration lessons. In this case, we have motion. The force that governs this motion is called the centripetal force.

So on the bob, you have:

1- Tension upwards

2- Weight and centripetal force downwards

thus, the tension has to be greater than mg. If you haven't taken the centripetal force yet you might want to go tell your teacher.

[ArielYao]

ariel what subjects do you have other than physics?

sl physics mandarin history

hl math english b economics