8.5 Vehicle safety

Question 1

A negative acceleration is equal to a…

Answer 1

…positive deceleration

Question 2

By expressing an acceleration or deceleration in terms of ______, the acceleration due to gravity, the force of the impact can then easily be related to the ______ of the vehicle.

Answer 2

g

weight

Question 3

The shorter the contact time…

Answer 3

…The greater the impact force for the same initial velocities of the two objects

Question 4

How can the impact time be worked out

Answer 4

Apply equation

s=1/2(u+v)t

Question 5

What is the work done by the impact force over an impact distance s equal to

Answer 5

The change of kinetic energy of the vehicle

Question 6

How can the impact force be calculated

Answer 6

F= change of kinetic energy/impact distance

or

F=ma

Question 7

When two vehicles collide,, they may or may not separate from each other after the collision.
If they remain tangled together, what happens in terms of forces

Answer 7

They exert forces on each other until they are moving at the same velocity

Question 8

How are cars designed

Answer 8

Increase the impact time to reduce the impact force

Therefore, the people are less affected

Question 9

How do vehicle bympers help

Answer 9

Give way a little in a low speed impact and so increase the impact time
Therefore, impact force is reduced
If the initial speed of impact is too high, the bumper or vehicle chassis is less likely to be damaged

Question 10

How do crumple zones help

Answer 10

The engine compartment of a car is designed to give way in a front-end impact
If it were rigid, impact time would be very short so impact force would be very large

Question 11

How do seat belts help

Answer 11

Restrains the wearer from crashing into the vehicle frame after the vehicle suddenly stops. The restraining force on the wearer is therefore much less than the impact force would be if they hit the frame
The wearer is stopped more gradually

Question 12

How does a collapsible steering wheel help

Answer 12

In a front-end impact, the seat belt restrains the driver without holding them rigidly.
If the driver makes contact with the steering wheel, the impact force is lessened as a result of the wheel collapsing in the impact

Question 13

How do airbags help

Answer 13

They reduce the force on a person as they act as a cushion to increase the impact time
The force of the impact is spread over the contact area which is greater than the contact area with a seat belt so the pressure on the body is less