# Mechanics A level problem, motion due to gravity

• Nov 10th 2012, 09:40 AM
mysur
Mechanics A level problem, motion due to gravity
A stone is thrown upwards with initial velocity of 24.5 ms-1 from a point 29.4 meters above the ground

(1) find the maximum height of the stone( above the ground)

(2) find the time when the stone hits the ground
(3) display the (t,v) graph for the motion of the stone ( up to the time when it his the ground)
(d) display a graph showing the height of the stone as a function of time.

ans whe I tried using s= u+v\t. With velocity = 0 and initial velocity = 24.5 I get 3 seconds bbut the answer give is t= 6 seconds and s= 60m please help me. Thank you
• Nov 10th 2012, 09:52 AM
skeeter
Re: Mechanics A level problem, motion due to gravity
(1) $\Delta y = \frac{v_{fy}^2 - v_{0y}^2}{2(-g)}$

$\Delta y = \frac{0 - 24.5^2}{-2g}$

$H = \Delta y + h_0$

(2) $\Delta y = v_{0y}t - \frac{1}{2}gt^2$

$-29.4 = 24.5t - \frac{1}{2}gt^2$

solve the quadratic for $t$

(3) graph ...

$v = 24.5 - gt$

$y = 29.4 + 24.5t - \frac{1}{2}t^2$
• Nov 10th 2012, 09:57 AM
mysur
Re: Mechanics A level problem, motion due to gravity
Thank you so very much I did calculation wrong. Thank you for your time