Momentum of a car

Problem

A car of mass $m = 1200\;\mathrm{kg}$ travels at $v = 45\;\mathrm{km/h}$. Calculate the magnitude of its momentum (remember to convert the velocity to m/s).

Solution

Momentum is $p = m\,v$, but the velocity must first be converted to SI units. An hour has $3600$ s and a kilometre has $1000$ m, so we divide by $3{,}6$: $v = 45\;\mathrm{km/h} = \frac{45}{3{,}6}\;\mathrm{m/s} = 12{,}5\;\mathrm{m/s}$ Now applying the definition of the magnitude of momentum: $p = m\,v = 1200\;\mathrm{kg}\cdot 12{,}5\;\mathrm{m/s}$ $p = 1{,}5\cdot 10^4\;\mathrm{kg\,m/s}$ $\ev{p = 1{,}5\cdot 10^4\;\mathrm{kg\,m/s}}$

Links

Topics: Quantità di moto e urti Concepts: Quantità di moto Skills: Impostazione simbolica