Chapter 4, Problem 1RCQ

Which has a greater momentum-a heavy truck at rest or a moving skateboard?

To determine

To Compare:

The momentum of a heavy truck at rest and a moving skateboard.

Answer to Problem 1RCQ

Solution:

A moving skateboard has more momentum than a heavy truck at rest. Because, object at rest has zero momentum.

Explanation of Solution

1) Concept:

Momentum is defined as “the product of the mass and the velocity of an object or particle” or “mass in motion”. Momentum is a vector quantity. It has both magnitude and direction. The S.I unit of momentum is $kg\cdot m/s$. Mass is defined as “a scientific measure of the amount of matter in an object”. It also stated that “the measure of the inertia of a material object”. Everything in the universe has mass. Mass is constant it means mass of the object is same everywhere. Moving objects have momentum. Suppose, an object is at rest, then the momentum of the object is zero. The momentum depends on two variables. Such as velocity and mass of the object or particle. For example, if an object has large mass and velocity, then the momentum of the object is large. If either one of the variables i.e. velocity or mass is large, then the momentum of the object is also large.

2) Formulae:

i) $p=mv$

Here, $p$-momentum; $m$-mass; $v$-velocity.

3) Given:

i) A heavy truck at rest.

ii) A skateboard is at moving.

iii) Momentum of moving skateboard and heavy truck at rest=?

4) Calculation:

$Momentum=Mass\times Velocity$.

i.e. $p=mv$

Find momentum of a heavy truck at rest:

$\begin{array}{rll}Momentum,p& =& mkg\times \text{ 0 }m/s\\ & =& 0\end{array}$

Velocity of the truck is zero, because it is at rest. So, its momentum is zero.

Find momentum of a moving skateboard:

$\begin{array}{rll}Momentum,p& =& mkg\times vm/s\\ & =& mvkg\cdot m/s.\end{array}$

Here, a skateboard is moving with some velocity. So, it has some momentum.

Suppose, direction is not an important factor, then the momentum is the product of the mass and the speed. i.e. $Momentum=Mass\times Speed$