Most of us know intuitively that in a head-on colli- sion between a large dump truck and a subcompact car, you are better off being in the truck than in the car. Why is this? Many people imagine that the collision force exerted on the car is much greater than that exerted on the truck. To substantiate this view, they point out that the car is crushed, whereas the truck is only dented. This idea of unequal forces, of course, is false; Newton’s third law tells us that both objects are acted upon by forces of the same magnitude. The truck suffers less damage because it is made of stronger metal. But what about the two driv- ers? Do they experience the same forces? To answer this question, suppose that each vehicle is initially moving at 8.00 m/s and that they undergo a perfectly inelastic head- on collision. Each driver has mass 80.0 kg. Including the masses of the drivers, the total masses of the vehicles are 800 kg for the car and 4 000 kg for the truck. If the colli- sion time is 0.120 s, what force does the seat belt exert on each driver?
Most of us know intuitively that in a head-on colli-
sion between a large dump truck and a subcompact car,
you are better off being in the truck than in the car. Why
is this? Many people imagine that the collision force
exerted on the car is much greater than that exerted on
the truck. To substantiate this view, they point out that the
car is crushed, whereas the truck is only dented. This idea
of unequal forces, of course, is false;
tells us that both objects are acted upon by forces of the
same magnitude. The truck suffers less damage because
it is made of stronger metal. But what about the two driv-
ers? Do they experience the same forces? To answer this
question, suppose that each vehicle is initially moving at
8.00 m/s and that they undergo a perfectly inelastic head-
on collision. Each driver has mass 80.0 kg. Including the
masses of the drivers, the total masses of the vehicles are
800 kg for the car and 4 000 kg for the truck. If the colli-
sion time is 0.120 s, what force does the seat belt exert on
each driver?
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