Bumpers on cars are not of much use in a collision. To see why, ...

[mydiamond]

Bumpers on cars are not of much use in a collision. To see why, calculate the average force a bumper would have to exert if it brought a 1200-kg car (a so-called compact model) to a rest in 15 cm
 
  when the car had an initial speed of 2.0 m/s (about 4.5 mph). (Bumpers are built with springs that compress to provide a stopping force without, hopefully, denting the metal.)
  A) 3.2  104 N
  B) 1.6  104 N
  C) 5.4  104 N
  D) 1.8  104 N
  E) 6.5  105 N

Question 2

A weightless spring of force constant 2.50 N/cm is 15.0 cm long when nothing is attached to it. It is now used to pull horizontally on a 12.5 kg box on a smooth horizontal floor.
 
  You observe that the box starts from rest and moves 96.0 cm during the first 1.60 s of its motion. How long is the spring during this motion?

[nyrave]

Answer to Question 1

B

Answer to Question 2

18.8 cm

[mydiamond]

Excellent

[gcook]

Gracias!