Mechanics Help (M1)

Hi, can someone help me with this mechanics question:

"A trampolinist bounces upwards and lands (at the same level) 1.8 seconds later. Find the initial velocity of the trampolinist and her greatest height."

Original post by Rhiannemahey

Hi, can someone help me with this mechanics question:

"A trampolinist bounces upwards and lands (at the same level) 1.8 seconds later. Find the initial velocity of the trampolinist and her greatest height."

What's confusing you about it? Have you attempted it yourself?

Reply 2

Rhiannemahey

OP

5

Yes I am not confident with M1 that is why.

What is the final velocity?

Reply 3

the bear

20

you need to use the SUVAT equations.

Reply 4

Rhiannemahey

OP

5

Okay would the final velocity be 0?

Original post by Rhiannemahey

Yes I am not confident with M1 that is why.

What is the final velocity?

Well consider what is actually going on. The person bounces up with an initial velocity

u

and while in the air the only force that is acting upon that person is gravity. This means we can model the situation as a projectile problem. Say that that the initial velocity is

u

then the velocity at time

t

is given by

v=u-gt

for the constant gravitational acceleration

g

. So what would the 'final' velocity be right before the person lands given that's a projectile upwards?

Reply 6

the bear

20

the velocity at the highest point will be 0

Reply 7

RogerOxon

21

Original post by Rhiannemahey

Hi, can someone help me with this mechanics question:

"A trampolinist bounces upwards and lands (at the same level) 1.8 seconds later. Find the initial velocity of the trampolinist and her greatest height."

Use

s=ut+\frac{at^2}{2}

The start, and end, points are at

s=0

. The equation above will yield two solutions,

t=0

(the start) and, the one you're given, when they come back down. Be careful with your signs - acceleration and speeds must be positive in the same direction.

If you can see / are allowed to, you can state that the greatest height will be at

t=0.9s

(half the time) and use

v=u+at

to calculate the initial speed (

v=0

at the top).

Mechanics Help (M1)

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