Question

A 40 Kg block is resting at a height of 5 m off the ground. If the block is released and falls to the ground, what is its total energy at a height of 2m? (g=10m/s2).
A) 0J
B) 400J
C) 2J
D) 6J
E) cannot be determined from given info.
@AllTehMaffs

Answer 1

right? @GTXMUQSIT

Answer 2

\[E = K + U\]
\[k = \frac{ 1 }{ 2 }mv^{2}\]
\[U = mgh\]
Where m = mass, v = velocity, h = height.

Answer 3

The total energy at any given point is given by that relation (E = K + U).
At the height of 5 meters, where the object is resting. The total kinetic energy is 0, because v=0. So E = K(5m) + U(5m) = U(5m)

Answer 4

At the height of 2 meters. E = K(2m) + U(2m) = U(5m)
You can calculate velocity using freefall equations.

Answer 5

but the total energy at that point has to be exactly the energy as when it strted falling

Answer 6

Yeah, but |mgh| = |(40(10)(5)| = 2000. Which is way to big.
I think it's asking for K(2m) or U(2m).

Answer 7

God I need to learn how to multiply

Answer 8

I think something is missing. It doesn't add up.

Answer 9

(Neither K or U)

Answer 10

blergh

Answer 11

@Lessis and @AllTehMaffs sir I couldn't find answer I apply the following formula
P.E=mgh so
P.E=40x10x2= 800 J which is not in options so I think option E is correct

Answer 12

@sarah786 do you know the anwser?

Answer 13

@CGGURUMANJUNATH

Answer 14

would you help

Answer 15

I think the answer isn't given - none of them make sense.

It asks for "total energy," which can't be any of the options.

\[ E_{initial}=E_{tot}=40kg*10m/s^2*5m = 2000J\]

Potential energy at 2m does not give the correct answer (like you saw) and

\[K = E_{tot} - U_{2m} = 2000J-(40*10*2)=1200J\]
so that's not the right answer either. It has to be E - there *is* enough information given, they just don't give the correct answer for you to choose ^_^

Answer 16

@AllTehMaffs thank you sir :D

Answer 17

maybe those are KJ
in which case C is the answer :P