# Mechanics

Watch
Announcements
#1
I proved for one case in which there will be no further collisions.But isn’t there another case in which B and C move in the same direction in which B will be at a lower speed therefore no colliding.
Last edited by Student 999; 1 month ago
0
#2
Bump
0
1 month ago
#3
B must be moving at a lower velocity than C after the collision.

Otherwise you'd have to invent the physics for B to pass through C.
Last edited by mqb2766; 1 month ago
1
#4
(Original post by mqb2766)
B must be moving at a lower velocity than C after the collision.

Otherwise you'd have to invent the physics for B to pass through C.
I know that,but I don’t know how to find the answer, is the value of k that I stated above also part of the range of values that I could be since it means that B will be stationary thus no further collisions
0
1 month ago
#5
(Original post by Student 999)
I know that,but I don’t know how to find the answer, is the value of k that I stated above also part of the range of values that I could be since it means that B will be stationary thus no further collisions
If B has negative velocity it will collide with A, so that is one limit (B post impact velocity = 0). This will occur if k is large and and effectively B bounces off a wall (heavy C). If k is small (light C), both B and C will move in the same direction after the collision and the velocity of C will be larger than B, so I can't see a lower limit for k, apart form the obvious physcial k>0.
0
#6
(Original post by mqb2766)
If B has negative velocity it will collide with A, so that is one limit (B post impact velocity = 0). This will occur if k is large and and effectively B bounces off a wall (heavy C). If k is small (light C), both B and C will move in the same direction after the collision and the velocity of C will be larger than B, so I can't see a lower limit for k, apart form the obvious physcial k>0.
So essentially k=8 as I proved and bigger than 0.This doesn’t answer the question in the range of values k must be.
0
1 month ago
#7
(Original post by Student 999)
So essentially k=8 as I proved and bigger than 0.This doesn’t answer the question in the range of values k must be.
Ive not checked your working, but you want the post impact velocity of B to be >= 0, assuming the pre impact velocity of B is postive. That gives you a range for k, as described in the previous response.
0
#8
(Original post by mqb2766)
Ive not checked your working, but you want the post impact velocity of B to be >= 0, assuming the pre impact velocity of B is postive. That gives you a range for k, as described in the previous response
It would make sense to find the lower limit of k by using inequalities whereby
velocity B<=velocity A ,after impact since they could coalesce
0
1 month ago
#9
(Original post by Student 999)
It would make sense to find the lower limit of k by using inequalities whereby
velocity B<=velocity A ,after impact since they could coalesce
I guess you need to understand (analyze the impact equation) why this is impossible, but the original reply is still valid.
0
#10
(Original post by mqb2766)
I guess you need to understand (analyze the impact equation) why this is impossible, but the original reply is still valid.
I’m so confused.What is the answer to the it??
0
1 month ago
#11
(Original post by Student 999)
I’m so confused.What is the answer to the it??
I don't know what your current answer is. You need to use the inequality in the velocity of B to get the inequality (upper limit) for k.

If you keep asking about a lower limit for k, you should do a thought experiment and understand why this won't occur.
0
#12
(Original post by mqb2766)
I don't know what your current answer is. You need to use the inequality in the velocity of B to get the inequality (upper limit) for k.

If you keep asking about a lower limit for k, you should do a thought experiment and understand why this won't occur.
However I tried doing an inequality but it came out to be messy
0
1 month ago
#13
(Original post by Student 999)
However I tried doing an inequality but it came out to be messy
Maybe try and make it less messy? If you're confident that k=8 corresponds to zero B velocity, it would be easy enough to argue that that would be the inequality boundary.
0
#14
(Original post by mqb2766)
Maybe try and make it less messy? If you're confident that k=8 corresponds to zero B velocity, it would be easy enough to argue that that would be the inequality boundary.
Could Veocity of C be the same as velocity of B
0
1 month ago
#15
(Original post by Student 999)
Could Veocity of C be the same as velocity of B
Doing thought experiments like these can be useful, but you should put the scenarios into the equation(s) and see what comes out.
0
#16
(Original post by mqb2766)
Doing thought experiments like these can be useful, but you should put the scenarios into the equation(s) and see what comes out.
You can’t put this into equations since I’m setting the boundaries of the values of what k could be therefore I’ll have to decide if it’s possible
0
#17
(Original post by mqb2766)
Doing thought experiments like these can be useful, but you should put the scenarios into the equation(s) and see what comes out.
0
1 month ago
#18
(Original post by Student 999)
You can’t put this into equations since I’m setting the boundaries of the values of what k could be therefore I’ll have to decide if it’s possible
Im really not sure what you're actually doing. If you set up the equations properly, there is no need to consider such scenarios. Having a read/review of momentum and restitution may help you unerstand such issues.
0
1 month ago
#19
(Original post by Student 999)
Can you post the full working, so the bits before you write v1 = ... (and what does it refer to etc).
Last edited by mqb2766; 1 month ago
0
#20
(Original post by mqb2766)
Can you post the full working, so the bits before you write v1 (and what does it refer to etc).
It’s on my very first post,I just simplified it so I get Velocity of B in terms of u and k.

V2 refers to velocity of C
Last edited by Student 999; 1 month ago
0
X

new posts
Back
to top
Latest
My Feed

### Oops, nobody has postedin the last few hours.

Why not re-start the conversation?

see more

### See more of what you like onThe Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

### Poll

Join the discussion

#### How would you feel if uni students needed to be double vaccinated to start in Autumn?

I'd feel reassured about my own health (32)
16.24%
I'd feel reassured my learning may be less disrupted by isolations/lockdowns (62)
31.47%
I'd feel less anxious about being around large groups (23)
11.68%
I don't mind if others are vaccinated or not (16)
8.12%
I'm concerned it may disadvantage some students (11)
5.58%
I think it's an unfair expectation (50)
25.38%
Something else (tell us in the thread) (3)
1.52%