free body diagram of crate; thermal detonator; 30kg mass on wheel: best approach?

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sonicflare9

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Consider a loot crate, at the top of a frictionless ramp. If the mass of the loot crate is 11.5kg and the ramp has a rise of 3m and a run of 4m, then compute the following.

a) Compute the free body diagram of the loot crate a time 0. (i.e. when the loot crate is at the top of the ramp.)
b) Compute the net force and the acceleration of the loot crate at time 0. Given the frictionless surface what do we know about the acceleration as the object moves down the ramp?
c) Consider the loot crate at it leaves the ramp and moves onto a flat surface that now has some friction. Compute the free body diagram for this situation. If the force of friction is proportional to
one quarter of the acceleration of the loot crate, calculate the new net force and acceleration at this point.
d) If we assume that the force of friction is constant after this point. How long will it take for the loot crate to stop moving?


Over a completely flat surface a thermal detonator (Star Wars) is thrown by a Wookiee (a member of the rebel alliance) towards a group of imperial stormtroopers. The thermal detonator always leaves the Wookiee’s hand with a speed of 100m/s and the thermal detonator has a mass of 3.2kg.
a) Suppose that the Stormtroopers are 500m away. What is the correct angle for the Wookiee to throw the thermal detonator so that it reaches the Stormtroopers.
b) What is the maximum distance the thermal detonator could travel?
c) If we know that there is an average wind force of 0.4N in the positive horizontal direction, then redo the above calculations taking into account this added force

3. Consider R2D2 (a droid) with mass 30kg riding on a Ferris wheel with diameter 25m, with a velocity of 2.8m/s.
a) Compute the free body diagram for R2D2 at the exact top, exact bottom and at both horizontal positions. Remember to include gravity. (Note: The forces act in different directions relative to the acceleration of the Ferris wheel. Where does the extra acceleration go?)
b) Give the net force and acceleration at each of these points. State any patterns that you see.
c) Give a set of equations for the general circular motion in gravity problem if we consider mass m, diameter d and velocity v.

any help is welcome
 
sonicflare9 said:
Consider a loot crate, at the top of a frictionless ramp. If the mass of the loot crate is 11.5kg and the ramp has a rise of 3m and a run of 4m, then compute the following.

a) Compute the free body diagram of the loot crate a time 0. (i.e. when the loot crate is at the top of the ramp.)
b) Compute the net force and the acceleration of the loot crate at time 0. Given the frictionless surface what do we know about the acceleration as the object moves down the ramp?
c) Consider the loot crate at it leaves the ramp and moves onto a flat surface that now has some friction. Compute the free body diagram for this situation. If the force of friction is proportional to
one quarter of the acceleration of the loot crate, calculate the new net force and acceleration at this point.
d) If we assume that the force of friction is constant after this point. How long will it take for the loot crate to stop moving?


Over a completely flat surface a thermal detonator (Star Wars) is thrown by a Wookiee (a member of the rebel alliance) towards a group of imperial stormtroopers. The thermal detonator always leaves the Wookiee’s hand with a speed of 100m/s and the thermal detonator has a mass of 3.2kg.
a) Suppose that the Stormtroopers are 500m away. What is the correct angle for the Wookiee to throw the thermal detonator so that it reaches the Stormtroopers.
b) What is the maximum distance the thermal detonator could travel?
c) If we know that there is an average wind force of 0.4N in the positive horizontal direction, then redo the above calculations taking into account this added force

3. Consider R2D2 (a droid) with mass 30kg riding on a Ferris wheel with diameter 25m, with a velocity of 2.8m/s.
a) Compute the free body diagram for R2D2 at the exact top, exact bottom and at both horizontal positions. Remember to include gravity. (Note: The forces act in different directions relative to the acceleration of the Ferris wheel. Where does the extra acceleration go?)
b) Give the net force and acceleration at each of these points. State any patterns that you see.
c) Give a set of equations for the general circular motion in gravity problem if we consider mass m, diameter d and velocity v.

any help is welcome
Click to expand...

for all 3,
1-what are you trying to find? (write it down)
2-draw a picture
3- label the picture with what the problem gives you
4- apply what you know to solve it.
 
sinx said:
for all 3,
1-what are you trying to find? (write it down)
2-draw a picture
3- label the picture with what the problem gives you
4- apply what you know to solve it.
Click to expand...

do you have any formulas for the questions
 
sonicflare9 said:
do you have any formulas for the questions
Click to expand...

no.
you are supposed to derive the equations yourself.
that is what i meant by; 'apply what you know to solve it.'
you 'apply what you know' to write equations, from the drawing you made and information they gave you.
from them you get the answer, 'to solve it'
If you have tried to derive equations, and are stuck, show your work and i will try to help.
 
Last edited:
sinx said:
no.
you are supposed to derive the equations yourself.
that is what i meant by; 'apply what you know to solve it.'
you 'apply what you know' to write equations, from the drawing you made and information they gave you.
from them you get the answer, 'to solve it'
If you have tried to derive equations, and are stuck, show your work and i will try to help.
Click to expand...

Same question! Thank you
Same question! Thank you
 
hieutrungpro said:
Same question! Thank you

a) Compute the free body diagram of the loot crate a time 0. (i.e. when the loot crate is at the top of the ramp.)
b) Compute the net force and the acceleration of the loot crate at time 0. Given the frictionless surface what do we know about the acceleration as the object moves down the ramp?
Click to expand...

example: how to solve these problems,
1-what are you trying to find? [Write down what it is you are trying to find, either word for word, or in your own words. This is most important.]
a) draw a free body diagram
b) Compute the net force and the acceleration of the loot crate at time 0.
c) Given the frictionless surface what do we know about the acceleration as the object moves down the ramp?

2-draw a picture and label it---the free-body-diagram
I don't know how to do this on computer, but have on paper.

3-apply what you know to solve it.
from the picture, (and you also know g=9.8m/s2)
force (down ramp) at time 0 = 11.5kg*9.8m/*sin(theta)
sin(theta)=3/5
net force (down ramp) at time 0=3/5(11.5)9.8N
acceleration (down ramp) at time 0=3/5(9.8)m/s2
the net force perpendicular to the ramp=0

c) Given the frictionless surface what do we know about the acceleration as the object moves down the ramp?
the acceleration is constant
 
Last edited:
sonicflare9 said:
Consider a loot crate, at the top of a frictionless ramp. If the mass of the loot crate is 11.5kg and the ramp has a rise of 3m and a run of 4m, then compute the following.
a) Compute the free body diagram of the loot crate a time 0. (i.e. when the loot crate is at the top of the ramp.)
b) Compute the net force and the acceleration of the loot crate at time 0. Given the frictionless surface what do we know about the acceleration as the object moves down the ramp?
Click to expand...

sonic, it has been long enough now for you to have worked thru this or be completely stumped. In case of the latter, I have worked the first problem out for you.

a) draw a free body diagram
I can't draw one on computer, but i did so on paper.
this is a must for solving these problems
the picture includes all information you are given.

b) compute force and acc. of loot crate at t=0
you have one force down the ramp, (there is no friction).
F=(mg)sin(theta)
F=(3/5)mg =force down the ramp.
F=ma.........3/5mg=ma
a=(3/5) =acceleration of crate at time=0
note: the mass cancels out.

sonicflare9 said:
do you have any formulas for the questions
Click to expand...
I assumed you knew these basic equations, in case not;
F=ma,
where F is the sum of forces in one direction, m=mass, a=acceleration.

other equations you need:
a=dv/dt
v=ds/dt
ads=vdv

where a=acceleration, v=velocity, t=time, s=distance

sonicflare9 said:
c) Consider the loot crate at it leaves the ramp and moves onto a flat surface that now has some friction. Compute the free body diagram for this situation. If the force of friction is proportional to
one quarter of the acceleration of the loot crate, calculate the new net force and acceleration at this point.
Click to expand...

F=0-(1/4)3/5mg (along the flat surface, you only have the friction force)
F=-(1/4)3/5mg (this is the net force)
F=ma
a=(-3/20)g
note: the mass cancels out.

sonicflare9 said:
d) If we assume that the force of friction is constant after this point. How long will it take for the loot crate to stop moving?
Click to expand...

a=dv/dt
v=ds/dt
ads=vdv

for a=3/5g, into ads=vdv, as=1/2v2 where s is length of ramp, v=velocity
v=(6g)1/2 =velocity at end of ramp
from adt=vdv, t=(20/3g)(6g)1/2 =time for crate to stop

time for crate to stop=5.2 secs.
 
sinx said:
sonic, it has been long enough now for you to have worked thru this or be completely stumped. In case of the latter, I have worked the first problem out for you.

a) draw a free body diagram
I can't draw one on computer, but i did so on paper.
this is a must for solving these problems
the picture includes all information you are given.

b) compute force and acc. of loot crate at t=0
you have one force down the ramp, (there is no friction).
F=(mg)sin(theta)
F=(3/5)mg =force down the ramp.
F=ma.........3/5mg=ma
a=(3/5) =acceleration of crate at time=0
note: the mass cancels out.


I assumed you knew these basic equations, in case not;
F=ma,
where F is the sum of forces in one direction, m=mass, a=acceleration.

other equations you need:
a=dv/dt
v=ds/dt
ads=vdv

where a=acceleration, v=velocity, t=time, s=distance



F=0-(1/4)3/5mg (along the flat surface, you only have the friction force)
F=-(1/4)3/5mg (this is the net force)
F=ma
a=(-3/20)g
note: the mass cancels out.



a=dv/dt
v=ds/dt
ads=vdv

for a=3/5g, into ads=vdv, as=1/2v2 where s is length of ramp, v=velocity
v=(6g)1/2 =velocity at end of ramp
from adt=vdv, t=(20/3g)(6g)1/2 =time for crate to stop

time for crate to stop=5.2 secs.
Click to expand...

what's d?
w
 
sinx said:
a=dv/dt
a=differential velocity/differential time
Click to expand...

F=0-(1/4)3/5mg (along the flat surface, you only have the friction force)
F=-(1/4)3/5mg (this is the net force)
F=ma
a=(-3/20)g

how do you get 3/5 and -3/20




 
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