Answer to Question #161191 in Mechanics | Relativity for Benjamin

Question

A truck traveling at 80 km/hr crashes into a brick wall without rebounding. We want to estimate the magnitude and direction of the force that the wall exerts on the truck. What physics concept will we use to solve this? How do we know? What do we need estimates for to do this? Finish the problem. Show all work.

Answer 1

Explanations & Calculations

Direction,

• What we know is that, the truck was moving hence it had some momentum which changed(came to zero) as collided with the wall.
• According to Sir Newton's first theorem, there has been an unbalanced net force acting on the truck during the collision therefore.
• Since the momentum change was such that it decreased over time, that force should be acting on the truck in the opposite direction to where it was heading.

Magnitude,

• Since there was a force there should be acceleration of the truck according to Newton's second theorem.
• Then it should be possible to apply the usual relationship—$\small F=m\large\frac{dv}{dt}$ — on the truck.
• Solving this gives an equation of force, velocity & time according to the nature of the motion of the truck— constant rate of decrement of velocity or varying rate.
• To estimate the force, the effective mass of the truck should be known.