Question

What is the speed of an object that travels from `( 7 , -4, 3 )` to `( -2 , 4, 9 )` over `4 s`?

Answer 1

`s=d/t=(13.45m)/(4s)=3.36` `ms^-1`

Explanation:

First find the distance between the points, assuming distances are in metres:

`r=sqrt((x_2-x_1)^2+(y_2-y_1)^2+(z_2-z_1)^2)`
`=sqrt(((-2)-7)^2+(4-(-4))^2+(9-3)^2)`
`=sqrt(-9^2+8^2+6^2)=sqrt(81+64+36)=sqrt181~~13.45` `m`

Then speed is just distance divided by time:

`s=d/t=13.45/4=3.36` `ms^-1`