Forces (5) - pt4

Question 1

What’s Newton’s second law of motion?

Answer 1

Resultant force (N) = acceleration (m/s*2) x mass (kg)
F = ma

Question 2

What’s inertial mass?

Answer 2

• It measures how difficult it is to change the velocity of an object
• Found using m = f / a
• it’s the ratio of force over acceleration

Question 3

What inertia?

Answer 3

The tendency to continue in the same state of motion (Newton’s 1st law)

Question 4

What’s Newton’s third law?

Answer 4

When 2 objects interact, the forces they exert on each other are equal and opposite

Question 5

What’s the stoping distance?

Answer 5

• it’s the sum of the thinking distance and braking distance
• the greater the speed of the vehicle, the greater the stopping distance
• the distance it takes a car to stop in an emergency

Question 6

What’s the thinking distance?

Answer 6

How far the car travels during the drivers reaction time (the time between the driver seeing a hazard and applying the brakes)

Question 7

What’s the braking distance?

Answer 7

The distance taken to stop under the braking force (once the brakes are applied)

Question 8

What are average braking distances for:

• 30mph
• 60mph
• 70mph

Answer 8

• 30mph = 14m
• 60mph= 55m
• 70mph = 75m

Question 9

What things can affect your thinking distance?

Answer 9

• your speed -the faster you’re going to travel while you’re reacting
• reaction time (alcohol, drugs, tiredness , distractions can effect this)

Question 10

What factors can affect your braking distance?

Answer 10

• speed (the faster a vehicle travels the longer it takes to stop)
• weather/ road surface(wet/icy, leaves or oil on the road, skidding)
• tyre conditions (if there worn down they won’t have grip)
• conditions of brakes (if they’re faulty could be dangerous)

Question 11

What’s dangerous about a large deceleration?

Answer 11

(Large braking forces lead to large deceleration)

• it can cause brakes to over heat
• could cause the vehicle to skid

Question 12

Explain how brakes work?

Answer 12

• brake pads are pressed onto the wheels causing friction, which causes work to be done
• the work done between the wheels and the brakes transfers energy from the kinetic energy stores of the wheels to the thermal energy stores of the brake
• the brakes increase in temperature

Question 13

What’s an average reaction time?

Answer 13

Everyone’s is different but it’s typically between 0.2 and 0.9s

Question 14

Explain why speed-stopping distance graph is linear but a speed-braking distance is curved?

Answer 14

• thinking distance stays constant. As a car speeds up the thinking distance increases at the same rate as speed.
• braking distance increases faster the more you speed up
• the stopping distance will be a combination of both

Question 15

What’s the formula to find momentum?

Answer 15

Momentum (kg m/s) = mass (kg) x velocity (m/s)

P = mv

Question 16

What conservation of momentum?

Answer 16

In a closed system, the total momentum before an event is equal to the total momentum after.

Question 17

What’s the formula to find force using momentum?

Answer 17

Force (N) = change in momentum (kg m/s) /change in time (s)

F = change in mv/change in time

Question 18

Explain what safety features a car has?

Answer 18

• crumple zones, increase the time take for the car to stop
• seat belts stretch increasing the time taken fir the wearer to stop
• air bags inflate before you hit the dashboard, the compressed air inside it slows you down more gradually than if you’d hit the dashboard
• increasing the time decreases the force because of F=change in mv/change in time