Question

A brick is lifted to a given height and then dropped to

the ground. Next, a second brick, which weighs twice as much as the first, is lifted just as high as the first and then it too is dropped to the ground. When the second brick strikes the ground it has
a) half as much kinetic energy
b) as much kinetic energy as the first
c) twice as much kinetic energy as the first
d) four times as much kinet- ic energy as the first

Answer 1

c) twice as much KE as the first

Step-by-step explanation:

GPE = mgh

KE = 1/2mv²

All the GPE converts to KE

1st brick GPE = mgh

h is the same for both bricks

Because the 2nd brick has 2x the mass as the first,

2nd brick GPE = (2m)gh

v of each brick just at it hits the ground is the same because all objects in free fall have the same acceleration, g, regardless of mass.

Conclusion: because 2nd brick has 2x the mass as the first brick, it has 2x the GPE, all of which converts to KE. Since v-final is same for both bricks, KE of 2nd brick is 2x the KE of the first brick because it has 2x the mass.

Answer 2

c

Step-by-step explanation: