# Change in kinetic energy

• forty
In summary, to find the change in kinetic energy when an object goes from moving at 10 m/s eastward to moving at 30 m/s southward, you simply subtract the initial kinetic energy from the final kinetic energy. This can be calculated using the formula KE = 1/2 * mass * velocity^2. No mass is needed since you are only finding the difference in kinetic energy.

#### forty

If an object goes from moving at 10 m/s eastward to moving at 30 m/s southward, how does its kinetic energy change?

If the object is to to change its velocity from east to south it would have stop all of its eastwards motion and then move in the southwards direction?

i have no idea if this is correct but i did the following

.5m(10)^2 + .5m(30)^2

and get 500m (mass is not given in the problem)

Any help would be greatly appreciated!

If an object goes from moving at 10 m/s eastward to moving at 30 m/s southward, how does its kinetic energy change?
This object is not moving in a one-dimension but in two-dimension. So, you can't just add/subtract them. You can use the Pythagorean theorem to find the change in velocity.

(mass is not given in the problem)
You don't need the mass. Since you are asked to find the change in kinetic and not the numerical values for the initial and final kinetic energy$$\Delta K=\frac{1}{2}m(v_{f}-f{i})^2$$

forty said:
If an object goes from moving at 10 m/s eastward to moving at 30 m/s southward, how does its kinetic energy change?

If the object is to to change its velocity from east to south it would have stop all of its eastwards motion and then move in the southwards direction?

Hi forty!

No … kinetic energy is a number, not a vector.

So it doesn't obey vector addition … it obeys ordinary addition!

What's the KE before? What's the KE after? How do you subtract one from the other?

so are you saying its just

.5m(30)^2 - .5m(10)^2 = 400m (J)

??

Yup!

(of course, the result will be in J only if the mass is in kg)

Sometimes physics really is that easy!

## 1. What is kinetic energy?

Kinetic energy is the energy an object possesses due to its motion.

## 2. How is kinetic energy calculated?

Kinetic energy is calculated using the equation KE = 1/2 * m * v^2, where m is the mass of the object and v is its velocity.

## 3. What causes a change in kinetic energy?

A change in kinetic energy can be caused by a change in mass, velocity, or both.

## 4. What is the relationship between kinetic energy and velocity?

The kinetic energy of an object is directly proportional to its velocity. This means that as the velocity increases, so does the kinetic energy.

## 5. How does friction affect the change in kinetic energy?

Friction can cause a decrease in kinetic energy by opposing the motion of an object and converting some of its kinetic energy into heat.