Magnitude, Direction of Momentum, & Velocity

[itsmarasilly]

Homework Statement

A compact car, mass 775 kg, is moving at 1.00 multiplied by 10^2 km/h toward the east.

(a) Find the magnitude and direction of its momentum.
(b) A second car, mass 2125 kg, has the same momentum. What is its velocity? (in km/h)

Homework Equations

The Attempt at a Solution

(a) 775 x 100 = 77,500 N s, to the east.. How do i convert this to kg m/s?

(b) 77,500 = mass x velocity
77,500 = 2125 x V
velocity = 77,500 / 2125
= 164,687,500 or 1.65 x 10^8 km/h

 

[rock.freak667]

For the units you multiplied you'd get kg km/h

to convert this to kgms^-1

you'd need to conert k (kilo) to 1000 and h (1 hour) to 360 seconds

thus you'd need to multiply by 1000/360

 

[thomate1]

I would like to point out that the units for momentum are kg m/s, not N s. To convert from N s to kg m/s, you can divide by the gravitational acceleration constant, g = 9.8 m/s^2. So, the momentum of the compact car would be 77,500 N s / 9.8 m/s^2 = 7,908 kg m/s to the east.

For part (b), we can use the equation for momentum again, but this time we know the mass and the momentum and are solving for velocity. So, we can rearrange the equation to solve for velocity: velocity = momentum / mass. Plugging in the values, we get velocity = 77,500 kg m/s / 2125 kg = 36.47 m/s. To convert this to km/h, we can multiply by 3.6, giving a final answer of 131.3 km/h.