Finding when particle at rest

3. A particle moves in a straight horizontal line such that its velocity, \(v \mathrm {~m} \mathrm {~s} ^ { - 1 }\), at time \(t\) seconds is given by \(v = 2 t ^ { 2 } - 9 t + 4\). Initially, the particle has displacement 9 m from a fixed point \(O\) on the line.

1. Find the initial velocity of the particle.
2. Show that the particle is at rest when \(t = 4\) and find the other value of \(t\) when it is at rest.
3. Find the displacement of the particle from \(O\) when \(t = 6\).

5. A particle \(P\) moves in a straight line with an acceleration of \(( 6 t - 10 ) \mathrm { m } \mathrm { s } ^ { - 2 }\) at time \(t\) seconds. Initially \(P\) is at \(O\), a fixed point on the line, and has velocity \(3 \mathrm {~ms} ^ { - 1 }\).

1. Find the values of \(t\) for which the velocity of \(P\) is zero.
2. Show that, during the first two seconds, \(P\) travels a distance of \(6 \frac { 26 } { 27 } \mathrm {~m}\).

2. A particle \(P\) moves along the \(x\)-axis such that its displacement, \(x\) metres, from the origin \(O\) at time \(t\) seconds is given by $$x = 2 + t - \frac { 1 } { 10 } \mathrm { e } ^ { t }$$

1. Find the distance of \(P\) from \(O\) when \(t = 0\).
2. Find, correct to 1 decimal place, the value of \(t\) when the velocity of \(P\) is zero.
   (4 marks)

3. A particle moves along a straight horizontal track such that its displacement, \(s\) metres, from a fixed point \(O\) on the line after \(t\) seconds is given by $$s = 2 t ^ { 3 } - 13 t ^ { 2 } + 20 t$$

1. Find the values of \(t\) for which the particle is at \(O\).
2. Find the values of \(t\) at which the particle comes instantaneously to rest.

1 A particle, P , has velocity \(v \mathrm {~m} \mathrm {~s} ^ { - 1 }\) at time \(t\) seconds given by \(\mathbf { v } = \left( \begin{array} { c } 6 \left( t ^ { 2 } - 3 t + 2 \right) \\ 2 ( 1 - t ) \\ 3 \left( t ^ { 2 } - 1 \right) \end{array} \right)\), where \(0 \leq t \leq 3\).

1. Show that there is just one time at which P is instantaneously at rest and state this value of \(t\). P has a mass of 5 kg and is acted on by a single force \(\mathbf { F }\) N.
2. Find \(\mathbf { F }\) when \(t = 2\).
3. Find an expression for the position, \(\mathbf { r } \mathrm { m }\), of P at time \(t \mathrm {~s}\), given that \(\mathbf { r } = \left( \begin{array} { c } - 5 \\ 2 \\ 6 \end{array} \right)\) when \(t = 0\).

1. A particle \(P\) moves on the \(x\)-axis. At time \(t\) seconds the velocity of \(P\) is \(v \mathrm {~m} \mathrm {~s} ^ { - 1 }\) in the direction of \(x\) increasing, where

$$v = ( t - 2 ) ( 3 t - 10 ) , \quad t \geqslant 0$$ When \(t = 0 , P\) is at the origin \(O\).

1. Find the acceleration of \(P\) at time \(t\) seconds.
2. Find the total distance travelled by \(P\) in the first 2 seconds of its motion.
3. Show that \(P\) never returns to \(O\), explaining your reasoning.

5. A particle \(P\) moves on the \(x\)-axis. The acceleration of \(P\) at time \(t\) seconds is \(( 4 t - 8 ) \mathrm { m } \mathrm { s } ^ { - 2 }\), measured in the direction of \(x\) increasing. The velocity of \(P\) at time \(t\) seconds is \(v \mathrm {~m} \mathrm {~s} ^ { - 1 }\). Given that \(v = 6\) when \(t = 0\), find

1. \(v\) in terms of \(t\),
2. the distance between the two points where \(P\) is instantaneously at rest.

1. A bird leaves its nest at time \(t = 0\) for a short flight along a straight line.

The bird then returns to its nest.
The bird is modelled as a particle moving in a straight horizontal line.
The distance, \(s\) metres, of the bird from its nest at time \(t\) seconds is given by $$s = \frac { 1 } { 10 } \left( t ^ { 4 } - 20 t ^ { 3 } + 100 t ^ { 2 } \right) , \quad \text { where } 0 \leqslant t \leqslant 10$$

1. Explain the restriction, \(0 \leqslant t \leqslant 10\)
2. Find the distance of the bird from the nest when the bird first comes to instantaneous rest.