Abullet of mass m is headed at horizontal speed v0 toward a block of mass 10m resting on a horizontal frictionless surface. the bullet strikes the block and comes to rest relative to the block somewhere deeply embedded inside the block. what average force did the block exert on the bullet if it took a time δt to stop the bullet?

Explanation:

The change in the momentum of an object is equal to the average force applied to that object in a given interval of time. We will apply this rule to the bigger mass, who is at rest initially.

can be found by the conservation of momentum:

Now the average force can be written in terms of v0, m, and Δt.

the old price per ounce is c/4.

the new price per ounce is c/3.6.

the ratio of the old price to the new one is

(c/4)/(c/3.6) = (c/c)×(3.6/4) = 0.9 . . = 9/10 . . "nine tenths" in either form