4.5.6.1.5 Acceleration

Question 1

Acceleration:

Answer 1

the rate of change of velocity

Question 2

Acceleration formula:

Answer 2

• acceleration (m/s2) = change in velocity (m/s) / time taken (s)
• a = v (final velocity) - u (initial velocity) / t

Question 3

constant force applied =

Answer 3

constant force applied = constant rate of acceleration/deacceleration

Question 4

How can the acceleration of an object be calculated from a velocity - time graph?

Answer 4

the acceleration of an object can be calculated from the gradient of a velocity - time graph

Question 5

How can the distance travelled be calculated using a velocity-time graph?

Answer 5

the distance travelled by an object (or displacement of an object) can be calculated by finding the area under the graph (measure when appropriate the area under a graph by counting the squares)

Question 6

How do you find the acceleration of a particular point on a curved velocity-time graph?

Answer 6

on a curved velocity-time graph to fund the gradient to find the acceleration you have to draw a tangent to the point on the curve at which you want to determine the acceleration

Question 7

If something accelerates, and it is dropping something at an equal rate, what happens to the distance between those things?

Answer 7

as something accelerates, if it is dropping something at an equal rate the distance between those things will become larger despite the rate of things being dropped the same as it is accelerating

Question 8

How can an object move at a constant speed but also accelerate at the same time?

Answer 8

It’s speed is constant however it can be changing direction meaning it’s velocity is constantly changing and as acceleration is the rate of change of velocity the object will be accelerating

Question 9

What is the acceleration like in uniform acceleration?

Answer 9

in uniform motion the acceleration is constant

Question 10

Equation for uniform acceleration:

Answer 10

Question 11

When can the equations of uniform acceleration only be used?

Answer 11

when an object travels with a constant uniform acceleration in a straight line

Question 12

What does any object near the Earth’s surface falling under gravity (no air resistance) have an acceleration of?

Answer 12

• 9.8m/s2
• when a ball is thrown upwards it decelerates so with an acceleration of -9.8m/s2 and then when it falls back down again it accelerates at a rate of 9.8m/s2

Question 13

What is an object that slows down doing?

Answer 13

decelerating

Question 14

What does drag/air resistance increase with?

Answer 14

Drag/air resistance increases with velocity

Question 15

What does it mean if the forces on an object are balanced?

Answer 15

• if the forces on an object are balanced, there is no resultant force
• the object either stays still or carries on at a constant velocity

Question 16

What will an object do if it has a resultant force?

Answer 16

then the object will accelerate or decelerate

Question 17

Describe the forces on a skydiver as he jumps out of a helicopter:

Answer 17

1. At the start there is only one force on the skydiver - resultant downwards force makes him accelerate - as weight is initially greater than air resistance
2. Increase in velocity causes his air resistance or drag to increase causes the resultant downward force to decrease - causes rate of acceleration to decrease
3. Air resistance increases until air resistance equals weight so there is no resultant farce so he stops accelerating and travels at constant velocity - this speed is called terminal velocity.
4. The his parachute opens which increases his surface are which increases his air resistance.
   
   1. Air resistance is greater than weight so there is now a resultant force upwards
   2. This causes the parachutist to decelerate which means that the velocity also decreases
   3. Air resistance and weight become equal again, travels at a new lower constant speed - reduced terminal velocity
5. When he hits the ground, it pushes up to make him decelerate quickly, when he stands on the ground, the ground pushes up on his feet - upward force is equal to his weight (so no resultant force

Question 18

Terminal velocity:

Answer 18

maximum speed of the object, reached when the forces moving the object are balanced by the frictional forces

Question 19

Describe the forces on a skydiver as he jumps out of a helicopter:

Answer 19

• When the sky diver step out of the plane the only force acting on her is her weight, which causes her to accelerate downwards
• As her velocity increases the air resistance (which acts upwards) increases
• This means the downward resultant force decreases which reduces her downward acceleration.
• This explains why the gradient of the graph decreases from 0 to 20s (as the gradient of a velocity-time graph is the acceleration)
• She continues to accelerate until the upward air resistance becomes equal to her weight, at which point the resultant force acting on her becomes zero
• This means that she no longer accelerates and travels at a constant velocity
• When she opens her parachute the size of the air resistance increases rapidly so that it becomes greater than her weight. This means that there is now a large upward resultant force.
• This large upward resultant causes a rapid deceleration which can be seen from the large negative gradient at 42s.
• As she decelerates her velocity decreases causing her air resistance to decrease as well
• This causes the upward resultant force to decrease, which causes the deceleration to decrease, which can be seen from the gradient becoming less negative.
• She continues to decelerate until the upward air resistance becomes equal to her weight, at which point the resultant force acting on her becomes zero
• This means that she no longer accelerates and travels at a new constant velocity