# Kinetic Energy/Momentum from change in direction and speed

• threewingedfury
In summary, a 2100 kg truck traveling north at 41 km/hr turns east and accelerates to 60 km/hr. The magnitude and direction of change in the truck's momentum can be found using the equation p = mv and resolving the vector system. The change in the truck's kinetic energy can be calculated using the formula KE = 1/2mv^2, with the change in KE being found by subtracting the initial KE (KE1) from the final KE (KE2). The units for KE are scalar, while the units for momentum are vector, so they need to be resolved separately. To resolve the momentum vector, you would multiply the mass by the velocity and take the difference between the initial and final values
threewingedfury
From a calculus based physics course:

A 2100 kg truck that travels north at 41 km/hr is turning east and accelerating to 60 km/hr
-What are the magnitudes and direction of change in the trucks momentum?
- What is the change in the trucks kinetic energy?

I need some help on steps - because I'm lost

momentum p = mv. Use this to work out the magnitudes of the vectors, then resolve the vector system.
K.E. = 1/2mv^2

would the change in KE be:
KE = .5mv^2
KE1 = .5(2100)(41km/hr * 0.277777778 m/s)^2
KE2 = .5(2100)(60km/hr * .277777778 m/s)^2
KE1-KE2 = 136192.132-291666.671
KE=-155474.54

and the momentum would be
p =mv
p1 = 2100*41km/hr
p2 = 2100*60km/hr
p1-p2 =-39900 kg*km/hr
Are those the right units? Or does it need to be in m/s?
Would the direction change be east? that's where I'm lost, or would it be the negative direction?

Last edited:
so am I right, or really wrong?

KE is right since it's just a scalar. Momentum is a vector so you need to resolve it.

but how exactly would you do that unless you multiply the mass to the velocity?

I tried the average of the 2 velocities, but that's not right

## 1. What is kinetic energy?

Kinetic energy is the energy an object possesses due to its motion. It is a scalar quantity that depends on the mass and velocity of an object.

## 2. How is kinetic energy related to change in direction and speed?

The change in direction and speed of an object affects its kinetic energy. When an object changes direction, its velocity changes, and therefore, its kinetic energy changes. Similarly, when an object changes speed, its kinetic energy also changes.

## 3. Can kinetic energy be negative?

No, kinetic energy cannot be negative. Since it is a scalar quantity, it only has magnitude and not direction. Therefore, it is always a positive value.

## 4. What is the formula for calculating kinetic energy?

The formula for calculating kinetic energy is KE = 1/2 * m * v^2, where m is the mass of the object and v is its velocity.

## 5. How does momentum play a role in kinetic energy?

Momentum is the product of an object's mass and velocity, and it is a vector quantity. The direction and magnitude of an object's momentum determine its kinetic energy. An object with a larger momentum will have a higher kinetic energy.

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