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**Unformatted text preview: **ConcepTest ConcepTest 9.1 9.1 Rolling in the Rain Rolling in the Rain 1) speeds up 1) speeds up 2) maintains constant speed 2) maintains constant speed 3) slows down 3) slows down 4) stops immediately 4) stops immediately An open cart rolls along a frictionless track while it is raining. As it rolls, what happens to the speed of the cart as the rain collects in it? (assume that the rain falls vertically into the box) Since the rain falls in vertically, it adds no momentum to the box, thus the box’s momentum is conserved. However, since the mass of the box slowly increases increases with the added rain, its velocity has to decrease decrease . ConcepTest ConcepTest 9.1 9.1 Rolling in the Rain Rolling in the Rain 1) speeds up 1) speeds up 2) maintains constant speed 2) maintains constant speed 3) slows down 3) slows down 4) stops immediately 4) stops immediately An open cart rolls along a frictionless track while it is raining. As it rolls, what happens to the speed of the cart as the rain collects in it? (assume that the rain falls vertically into the box) Follow-up: Follow-up: What happens to the cart when it stops raining? What happens to the cart when it stops raining? A net force of 200 N acts on a 100-kg boulder, and a force of the same magnitude acts on a 130-g pebble. How does the rate of change of the boulder’s momentum compare to the rate of change of the pebble’s momentum? 1) greater than 2) less than 3) equal to ConcepTest ConcepTest 9.3a 9.3a Momentum and Force Momentum and Force A net force of 200 N acts on a 100-kg boulder, and a force of the same magnitude acts on a 130-g pebble. How does the rate of change of the boulder’s momentum compare to the rate of change of the pebble’s momentum? 1) greater than 2) less than 3) equal to The rate of change of momentum is, in fact, the force. Remember that F = Δ p / Δ t . Since the force exerted on the boulder and the pebble is the same, then the rate of change of momentum is the same....

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