1. 10.7 Safety first Q1. Impact force = change in momentum impact time
Impact force ( decreases) = change in momentum (stays the same)
impact time ( increases )
The safety helmet increase the time taken to slow down and stop.
It also increases the surface area reducing the pressure on the head and the chance of a cracked skull.
Q2. a. Rear facing seats are safer for babies. There is less chance of flying out of the seat between the straps. The cushion material ( polystyrene and soft foam), increases the impact time and also greatly increase the surface area in contact with the baby further reducing the pressure and damage caused by straps across the chest.
Q2b. An air bag has the same effect as above .

2. Q3. Impact force = ∆ momentum ∆ time
If the vehicle stops suddenly, the change in momentum has to occur in a short time so any impact force is high causing injury.
Wearing a seat belt increases the impact time and therefore the impact force on the body. It also reduces the pressure by giving a greater area of contact from the belt rather than hitting the windscreen directly.
Q4.
After Impact
Before Impact

3. Momentum of car and lorry immediately after impact
Q4.
After Impact
Before Impact
= ( Massc + Mass L) x V
= ( ) kg x 9m/s
Momentum of car and lorry immediately after impact
= kg x 9m/s
= ,100 kgm/s

4. just before the collision
Q4b.
Q4.
Assume lorry is moving slowly across the road at about 3m/s. This eastward momentum does not affect the Northwards momentum.
After Impact
Before Impact b)
To find velocity of car
just before the collision
For collisions: p before = p after
(750kg x Vc m/s) + ( 2100kg x 0 m/s) = ,100 kgm/s
(750kg x Vc m/s) = ,100 kgm/s
34.8 m/s is about 77 mph
Car was exceeding
the speed limit of 60mph
Vc m/s = ,100 kgm/s
= m/s kg