Question

A body is thrown up with a velocity of 29.23ms^-1 distance travelled in the last second of upward motion is?

Answer 1

Assuming the body will fall and terminal velocity is not reached, find out the distance it will travel up by using
v² = u²+2as where v² is 0 and a is -9.81
Then use the the same distance again in the same equation to find the ending velocity v
v² = u²+2as where u² is 0 and a is 9.81
Note :- Dont mess up the signs of acceleration

Answer 2

I got 41.28...

Answer 3

If you're talking about ending velocity then incorrect, if you're talking about displacement you're close to correct answer

Answer 4

I got S to be 43.49 m ...but thats not an option...

Answer 5

S is correct. But you have to find out v

Answer 6

i got v 29.19ms^-1

Answer 7

It should be 29.23 exactly the same as initial velocity. Can you figure out why? (Hint. Consider energies)

Answer 8

No loss of energy?

Answer 9

Okay yes but can you figure out a relation of absence of loss has to do with equality of u=v?

Answer 10

How do I do so?

Answer 11

Okay so when the ball rises, the kinetic energy converts to gravitational potential energy right? And because no resistances are mentioned, kinetic energy is converted completely to GPE. Agree?

Answer 12

Yes.

Answer 13

So after stopping in the air, the GPE starts to get converted to KE. When the distance risen matched distance fallen, the GPE is converted completely to KE. Agree?

Answer 14

Okay?

Answer 15

So we can conclude that KE at start = Gain in GPE = KE at end
KE at start = KE at end
V at start² x 0.5 x m = V at end² x 0.5 x m
V at start²= V at end²
V at start= V at end

I hope you aren't confused.

Answer 16

ya okay...what next?

Answer 17

This is the proof that Velocity will remain same if the distance fallen = distance risen

Answer 18

However, since the question is ambiguous the upper answer was for if the ball starts to fall back
But what about if they are asking the final velocity of the ball assuming the ball doesn't fall back? Simple. Because the acceleration is in opposite direction to velocity, the smallest value the velocity can reach is 0 and thus the final velocity will be 0.

I hope this clears up your confusions

Answer 19

They have asked the displacement ....

Answer 20

That's the trick. I am sorry I didn't explain it before.
Distance traveled in a second = Velocity.
Distance traveled in the last second = Ending Velocity

Answer 21

....
29.23 is not an option....

Answer 22

Can you show us the options

Answer 23

2.3
6
9.8
4.9

Answer 24

Are you sure the wordings of the question is correct?

Answer 25

yes,yes i am...

Answer 26

Well the question is incorrect.
Reasons.
1:- They haven't defined the time limit from which we can conclude what exactly is the last second
2:- They haven't defined the displacement that will occur( displacement till v= 0) isn't a valid assumption here since the choices doesn't contain 0 as an option

Answer 27

If you had provided the choices beforehand, I would've given the same conclusion earlier. Apologies for wasting your time