# Physics - Recall for Chapter 3: Motion

> Source: https://ollybritton.com/notes/a-level/physics/recall-questions/chapter-3-motion/ · Updated: 2021-08-03 · Tags: physics, school, motion, recall-questions

## Recall Questions
##### Define displacement??
Distrance travelled in a particular direction.

##### Define velocity??
Rate of change of displacement.

##### Define acceleration??
Rate of change of velocity.

##### State the units of acceleration??
$$
ms^{-2}
$$

##### Define instantaneous speed??
Displacement $\Delta s$, divided by time for a very short time interval, $\Delta t$.

##### Define average speed??
Total displacement divided by the total time for journey.

##### What does the gradient of a displacement-time graph represent??
Instantaneous velocity.

##### What does the gradient of a velocity-time graph represent??
Acceleration

##### What assumption is made when using the SUVAT equations??
Acceleration is constant/uniform.

##### How is the total stopping distance of a car calculated??
stopping distance = thinking distance + braking distance

##### Define thinking distance??
The distance travelled by a vehicle between the driver recognising a reason to stop and applying the brakes.

##### Define braking distance??
The distance travelled by a vehicle from the instant the brakes are applied to when the vehicle stops.

##### How does thinking distance depend on the speed of the vehicle??
Thinking distance depends on reaction time, so thinking distance is proportional to speed.

##### How does braking distance depend on the speed of the vehicle??
Braking distance is proportional to $\text{speed}^2$.

##### Describe how acceleration due to gravity $g$ can be determined by experiment (long)??
Drop an object from a known height and time how long it takes to fall using a stopwatch/light gates/electromagnet and trap door. Repeat for different heights and then plot a graph of height against $\text{time}^2$. Gradient is $\frac{g}{2}$.

##### What is a projectile??
An object acted upon only by weight, so its acceleration is $9.8ms^{-2}$.

##### How can we solve projectile problems??
By treating horizontal and vertical motion seperately.

##### What assumption is usually made when solving projectile motion problems on Earth?
Air resitance is ignored.

##### Describe and explain the horizontal motion of a projectile??
Horizontal velocity remains constant as no forces are acting horizontally.

##### Describe and explain the veritcal motion of a projectile??
Vertical acceleration is $9.8ms^{2}$ downwards as the only force acting is the weight of the object.

##### What is the horizontal component of the initial velocity of a projectile launched at velocity $u$ and angle $\theta$ to the horizontal??
$u\cos \theta$

##### What is the vertical component of the initial velocity of a projectile launched at velocity $u$ and angle $\theta$ to the horizontal??
$u\sin \theta$

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