You are Here: Home >< Physics

# Motion in a vertical plan question

Announcements Posted on
Why bother with a post grad? Are they even worth it? Have your say! 26-10-2016
1. a stone is dropped from the top of a tower. 3 seconds later another stone is thrown downwards from the same point at 35m/s. if they hit the ground at the same time find the height of the tower.

This is technically a mechanics 1 question but im sure the physics forum will have no trouble
2. S = ?
u = 35 ms^-1
v =
a = 9.8 ms^-2 (because the particle is being dropped downwards we take gravity to be positive)
t = 3s

Now, use an equation that coincides with all of our measurements: in order to find s (the displacement).
3. (Original post by TarotOfMagic)
S = ?
u = 35 ms^-1
v =
a = 9.8 ms^-2 (because the particle is being dropped downwards we take gravity to be positive)
t = 3s

Now, use an equation that coincides with all of our measurements: in order to find s (the displacement).
I already tried that. Like this:

S = ut + 1/2at^2
S = 35 (3) + 4.9(3^2)
S = 105 + 44.1
S = 149.5 m

But according to the answer this is wrong it should be 579.5 m

4. (Original post by hals)
a stone is dropped from the top of a tower. 3 seconds later another stone is thrown downwards from the same point at 35m/s. if they hit the ground at the same time find the height of the tower.

This is technically a mechanics 1 question but im sure the physics forum will have no trouble
the struggle is real
5. (Original post by u.sha)
the struggle is real
Oh look we have matching avatars 😁
6. (Original post by TarotOfMagic)
S = ?
u = 35 ms^-1
v =
a = 9.8 ms^-2 (because the particle is being dropped downwards we take gravity to be positive)
t = 3s

Now, use an equation that coincides with all of our measurements: in order to find s (the displacement).
You're an idiot. The stone moving at 35 m/s is dropped 3 seconds after the first, it doesn't take 3 seconds to reach the floor.
(Original post by hals)
a stone is dropped from the top of a tower. 3 seconds later another stone is thrown downwards from the same point at 35 m/s. if they hit the ground at the same time find the height of the tower.

This is technically a mechanics 1 question but im sure the physics forum will have no trouble
For the first stone,
s=
u=0
v=
a=9.8
t=t+3

For the second stone
s=
u=35
v
a=9.8
t=t

Equate the two displacements to find time, then find displacement using that value of t
7. (Original post by an_atheist)
You're an idiot. The stone moving at 35 m/s is dropped 3 seconds after the first, it doesn't take 3 seconds to reach the floor.

For the first stone,
s=
u=0
v=
a=9.8
t=t+3

For the second stone
s=
u=35
v
a=9.8
t=t

Equate the two displacements to find time, then find displacement using that value of t
Thanks
Shouldn't t=t-3 for the 1st stone because it happens before the 2nd one -.-

P.s. That idiot remark was unnecessary but ill let it slide because you tried to help
8. (Original post by hals)
Thanks
Shouldn't t=t-3 for the 1st stone because it happens before the 2nd one -.-

P.s. That idiot remark was unnecessary but ill let it slide because you tried to help
**** you are correct. Sorry about the idiot thing, it annoys me when people (inclding myself) manage to mess up easy maths based problems
9. (Original post by an_atheist)
**** you are correct. Sorry about the idiot thing, it annoys me when people (inclding myself) manage to mess up easy maths based problems
Apology accepted lol. Obviously that 1st method i tried wouldnt have worked because t=3 was not the actual time of fall but then i didnt know wht else to do and came on here after trying that invalid method
10. (Original post by hals)
Apology accepted lol. Obviously that 1st method i tried wouldnt have worked because t=3 was not the actual time of fall but then i didnt know wht else to do and came on here after trying that invalid method
Nope, it is t+3 for the first stone. IF the second stone is falling for a time t, the first stone was released 3 seconds earlier, and was falling for t+3 seconds

Got 579.5m for the height of the tower.
11. (Original post by an_atheist)
**** you are correct. Sorry about the idiot thing, it annoys me when people (inclding myself) manage to mess up easy maths based problems
Irony, at its finest.

## Register

Thanks for posting! You just need to create an account in order to submit the post
1. this can't be left blank
2. this can't be left blank
3. this can't be left blank

6 characters or longer with both numbers and letters is safer

4. this can't be left empty
1. Oops, you need to agree to our Ts&Cs to register

Updated: October 2, 2016
TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Today on TSR

### University open days

Is it worth going? Find out here

### How to cope with a heavy workload

Poll
Study resources

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.