bumblebee123
Junior Member
- Joined
- Jan 3, 2018
- Messages
- 200
I don't know if I've done the right method, even though I have the right answer. Can anyone check my method?
question: a body is moving in a straight line which passes through a fixed point O. The displacement, x metres, of the body from O at time t seconds is given by
x= t^3 + 3t^2 - 9t
a) find an expression for the velocity, v m/s, at the time t seconds
I managed to do this: v = 3t^2 + 6t - 9
b) find the acceleration when the body is instantaneously at rest
I thought this would be when the velocity = 0
so 0 = 3t^2 + 6t - 9
0 = ( 3t - 3 ) ( t + 3 )
t = 1 or t= -3
however, t must = 1 because it can't be negative
so if I put this into the acceleration equation: a = 6t + 6
a = 6 + 6
a = 12 m/s^-2 which is correct
did I do it right? thanks!
question: a body is moving in a straight line which passes through a fixed point O. The displacement, x metres, of the body from O at time t seconds is given by
x= t^3 + 3t^2 - 9t
a) find an expression for the velocity, v m/s, at the time t seconds
I managed to do this: v = 3t^2 + 6t - 9
b) find the acceleration when the body is instantaneously at rest
I thought this would be when the velocity = 0
so 0 = 3t^2 + 6t - 9
0 = ( 3t - 3 ) ( t + 3 )
t = 1 or t= -3
however, t must = 1 because it can't be negative
so if I put this into the acceleration equation: a = 6t + 6
a = 6 + 6
a = 12 m/s^-2 which is correct
did I do it right? thanks!