velocity/speed + momentum

What is the speed of sound in air?

330m/s

What is the approx. speed of walking?

1.5m/s

What is the approx. speed of running?

3m/s

What is the approx. speed of cycling?

6m/s

What is the approx speed of a car?

25m/s

What is the approx speed of a train?

55m/s

What is the approx speed of a plane?

250m/s

Define acceleration + What do we call negative acceleration?

• Rate of change in velocity

• deceleration

In the velocity equation, what does u and v refer to?

u: initial velocity

v: final velocity

What information can you gather from distance-time graphs? (4)

• gradient = speed

• flat line = stationary

• curved line = acceleration

• straight line = constant speed

What information can you gather from a velocity-time graph? (3)

• acceleration of an exact point = draw tangent

• distance = area under curve

• flat line = constant velocity

When you let go of an object, why does it fall towards earth? Answer in terms of acceleration (2)

• gravity exerts weight on the object

• causes it to accelerate towards earth (moving downwards)

What is meant by terminal velocity? (2)

• air resistance and weight reach equillibrium

• maximum velocity object can reach falling through a fluid

Why do objects reach terminal velocity? (4)

• velocity of object increases as it accelerates

• force of air resistance will also increase

• forces will eventually reach equilibrium

• no more acceleration and velocity remains constant

Newton’s first law

a resultant force is needed to change the motion of an object

Newton’s second law (include equation)

acceleration of an object is proportional to the resultant force acting on it, and is inversely proportional to the object’s mass (f=ma)

Newton’s third law

When two objects interact, they exert equal and opposite forces on each other (this also called normal contact force)

What is stopping distance? (3)

• total distance a car travels from moment driver first notices obstruction to when the car stops

• includes thinking distance (distance car travels between driver noticing and applying brakes)

• and braking distance (distance car travels between applying breaks and car stops moving)

3 factors that affect drivers reaction time/thinking time

• tiredness

• sobriety

• distraction

What factor affects both thinking and braking distance?

speed of the car

5 factors that affect braking distance

• quality of brakes

• quality of tyres

• road surface

• speed of vehicle

• mass of vehicle

If a vehicle drives twice as fast, what happens to braking distance?

increases by 4 times (square of speed)

Is momentum a vector or scalar quantity? + Units for momentum?

vector, kgm/s

What is the conservation of momentum principle?

total momentum before a collision is the same as total momentum after the collision

Using ideas of momentum and force, explain why car crashes cause injury to passengers? (3)

• car and passengers decelerate rapidly

• experience large forces because of the rapid change in momentum

• these large forces cause injury

3 safety features of modern cars which reduce harm to passengers + how

• seatbelts (stretches to increase time taken for momentum to reach zero, so reduces force on the body)

• air bags (soft surface to collide with, flexible so increase time taken for momentum to reach zero, reducing force on body)

• crumple zones (areas of vehicle designed to crumple in a controlled way, increases time taken for momentum to reach zero, reducing force on body)