# Homework Help: Can I use a dot product of accel. and vel. to find displace.

1. Nov 7, 2015

### Jamiemma1995

1. The problem statement, all variables and given/known data at what initial speed would a projectile have to start at when ejected at 35 degrees to the horizontal from a point A to a point B which is 9.4km distance away in the horizontal and 3.3km below it. taking g as 10m/s

2. Relevant equations
I'm not really sure if these equations are relevant because if I can't use the dot product they are not

A⋅B=ABcosθ

3. The attempt at a solution so first of all the resultant displacement between the x and y is 9.96 km so the I said that v⋅a=vacos55 (as the angle between the acceleration which is straight down and v is 55) and because I'm assuming that the dot product between v and a is displacement I said 9960=v10cos55 and got v=1736.5 m/s

2. Nov 7, 2015

### Jamiemma1995

I just realised of course displacement is also a vector, which was pretty silly of me still any help with the actual question would be much appreciated