what is its kinetic energy?

Question

An object of mass 5 kg is dropped from a height of 10m. What will be its kinetic energy after it has fallen 4m?

what is its kinetic energy just before it hits the ground?

Answer 1

The kinetic energy for this problem is the amount of energy the object has as it falls 4m. This is actually equal to the potential energy before the object is dropped.

You're probably thinking that E = (1/2)mv^2

However, the easier way to solve this is with E = mgh

So,
E = mgh
m = 5 kg
g = 9.81 m/s/s
h = 4 m

E = (5 kg) (9.81 m/s/s) (4 m)
E = 196.2 J

Answer 2

Kinetic energy is the energy of a body in motion (i.e., it must have some velocity).

In this problem, the body starts from rest.

Its kinetic energy is initially zero.

After it begins to move its speed increases and hence its kinetic energy.

The force that causes it to move is mg.

The distance through which it has moved is 4m.

Work done on the body is Fore x distance

= 5 x 9.8 x 4 = 196 joule.

This is the energy possessed by the object as kinetic energy.
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Another way of doing this problem is to find its velocity when it moves through 4m and calculate its kinetic energy.

Using the formula V^2 = U^2 + 2as and noting that U =0 , a = 9.8m/s^2 and s = 4m ,

V^2 = 2 x 9.8 x 4
The kinetic energy is 0.5 m V^2 = 0.5 x 5 x 2 x 9.8 x 4

= 5 x 9.8 x 4 same as the one calculated previously.
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Answer 3

Now that you have the TE figured out for the Conservation of Energy Theory, you can find the proportion of PE and KE at any point in the object's fall. The TE will always be the same. Sooo....

If you move some variables around in the equation for Cons of En, you get:

TE - PE = KE

You know your TE. Now just use your new variable (4m) with the same mass to produce your new PE for this new dynamic and subtract it from your always constant TE and here is your new KE at 4m.
Let me know if I helped.

Rogue

Answer 4

KE=1/2(mv^2)

so you need to calculate the velocity of an object in free fall for 6 m

x=1/2at^2+vt

4m=1/2(9.8m/s^2)t^2+0

t=(8/9.8)^.5
t=0.904
4m/0.904=v=4.427m/s

KE=(1/2)(5kg)(4.427m/s)(4.427m/s)= approx. 49 Newton meters or approx 49 Joules

The science teacher gets an F for using the final height of the object as the velocity

The one that uses Potential energy forgets to calculate the total energy of the system at 10m then subtract the PE remaining at 4 m to find the energy converted to KE.

Answer 5

Kinetic energy is the retained energy of an object that was required to accelerate it to it's present state. Once the object strikes the ground it becomes negative energy.

Answer 6

The form of energy associatedwith the speed of an object. Its equation is: KE=1/2mv2(squared); or kinetic energy= ? mass x velocity squared. (It is obvious from the formula that increasing clubhead velocity has more potential for producing distance than increasing the clubhead weight.)

Answer 7

I'm glad I didn't have science teacher in my first physics class. If so I'd probably be flipping burgers now.

And SteveA8 gets an F for calculating average velocity and using it as if it were the final velocity. And for saying Silas was wrong - Silas was right.

pearlsawm... also did it well.

Answer 8

KE=1/2 mv^
KE=1/2(5)(4*4)
40Kgm^ or joules