Question

force and motion end - of - unit assessment (continued)

crash 1

crash 2

1. scott and james work at a grocery store. after the grocery store closed, they were playing a game with a shopping cart and scotts skateboard. they crashed the skateboard and the shopping cart two times. the shopping cart had more mass in crash 2 than it did in crash 1. use the information in the diagram to answer.

in which crash did the skateboard experience a stronger force? why?

a. the skateboard did not experience a force; only the shopping cart experienced a force in the crashes.

b. crash 2; the force on the cart was stronger in this crash, so the force on the skateboard was also stronger.

c. the diagram doesnt tell you anything about the force on the skateboard. it only gives information about the force on the shopping cart.

d. the skateboard experienced the same force in both crashes. the shopping cart changed speed by the same amount in each crash, so the force on the skateboard was the same each time.

Explanation:

According to Newton's third law of motion, when two objects interact, the forces they exert on each other are equal in magnitude and opposite in direction. In Crash 2, the shopping cart has more mass. Using Newton's second law \(F = ma\) (where \(F\) is force, \(m\) is mass, and \(a\) is acceleration), for the same change in speed (acceleration \(a=\frac{\Delta v}{\Delta t}\), and \(\Delta v = 3m/s\) in both cases), a larger - mass cart requires a larger force to achieve the same change in speed. Since the force on the cart is stronger in Crash 2, the force on the skateboard (which is the reaction force to the force the skateboard exerts on the cart) is also stronger in Crash 2.

Answer:

B. Crash 2; the force on the cart was stronger in this crash, so the force on the skateboard was also stronger.