# Find its maximum height and initial velocity

1. Oct 3, 2004

### wolfson_1123

Hello i have been able to do 7 out of 8 question on my linear motion questions, but this last question number 8, is proving difficult. I don't know whether the tutor has made a mistake (as the answers are typed at the bottom) so if you could be of help i would be very glad ty.

I am using s = u.t + 0.5.a.t^2

and v = U + a.t

but neither bring up the correct answers:

8. A pistol pellet is fired vertically upwards and lands back at its firing point
8 seconds later. Neglecting air resistance, and assuming the acceleration due to gravity is g = 9.81 m/s2 downwards ! find its maximum height and initial velocity.
[answers: 78.5 m , 39.2 m/s]

Ty every so much :-)

2. Oct 3, 2004

### poolwin2001

Welcome to PF
The bullet starts with velocity v,slows down due to gravity,and attains v=0 at max height.Then it picks up speed(due to gravity) and reaches down with total velocity v.
So time taken to attain v=0 is 8/2=4s.
I plugged this into the eqn and got the given answer.
Similarly,height reached is when velocity becomes 0,I got the given answer with the eqn you gave.
I think you tried t=8s.I hope you understood.
regards

Last edited: Oct 3, 2004