# Questions and Answers

# Your Questions About X1

Donald asks…

## In MS Works 9 database what is the formula to sum a column of figures?

Of course the formula goes in the box at the bottom of the field.

Sum (above) and = **x1**=x2=x3 and the like in several variations have been tried without success. Very strange because there is no problem at all in ‘Word’ and Spreadsheet in summing a column.

### Administrator answers:

SELECT SUM(ColumnName) AS AliasName FROM TABLE_NAME

Jenny asks…

## What is the initial velocity? what is initial angle relative to the horizontal? what is height at top of path?

A ball is thrown into the air from ground level. After a time t = 2 s, the ball has traveled to a position **x1** = 29 m to the right of and y1 = 13 m up from where it was thrown (at this time, the x and y components of the ball’s velocity are still positive). The axes show the x and y directions to be considered positive.

### Administrator answers:

See for a questions on projectile motion we need 2 consider 2 main things

1)The body moves in a plane such that its velocity vector has a horizontal component Vx and a vertical component Vy.

2)The horizontal velocity remains constant (horizontal acceleration is zero) while vertical velocity changes coz of acceleration due to gravity)

We apply the same equations as for 1 dimensional motion just with the difference of considering 2 velocity components

Angle of projection = Q

Vo= initial velocity

Vy=VoSinQ

Vx=VoCosQ

Hence x=29=0+VoCosQ X2 – eq 1

y=13=VoSinQX2-1/2(g X4) – eq2

solving 1 and 2

=>tanQ=(32.6/29)

From here we get initial angle and using its value in eq1 we get Vo.

At the maximum height Vy-0.This explains why this is the max height as after this height Vy becomes negative (the direction of vertical motion changes) and the body starts falling down

considering vertical motion

Vy^2=(VoSinQ)^2 – 2gY

Y is the vertical displacement

At max height Vy=0

=>

Y=(VoSinQ)^2/2g

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