3.1 | Momentum and Impulse

"Mass in motion" is one definition for:

• momentum

• impulse

• power

• impact

Answer explanation

The formula for momentum is

$p\ =\ m\cdot v$

Mass x Velocity is "mass in motion".

Tags

NGSS.HS-PS2-2

A change in momentum from applying a force for a certain time is:

• momentum

• impulse

• power

• impact

Answer explanation

The formula for impulse is

$J\ =\ F\cdot t$
Impulses create changes in momentum.

The equation for momentum is:

• $\overrightarrow{p}=m\cdot\overrightarrow{v}$

• $\overrightarrow{F}=m\cdot\overrightarrow{a}$

• $\overrightarrow{J}=\overrightarrow{F}\cdot t$

• $\overrightarrow{\Delta v}=\overrightarrow{v_f}-\overrightarrow{v_i}$

Answer explanation

Remember: Momentum is "mass in motion" so the equation needs to have mass and velocity (motion).

Tags

NGSS.HS-PS2-2

Which of the expressions below can be used to calculate impulse? (Choose all that apply.)

•  $m\cdot\overrightarrow{\Delta v}$ 

•  $m\cdot\overrightarrow{a}$ 

•  $\overrightarrow{F}\cdot t$ 

•  $\overrightarrow{v_f}-\overrightarrow{v_i}$ 

Answer explanation

Because impulses causes changes in momentum, you can use the equation for either of those to calculate impulse.

A cart with a mass of 15 kg has a velocity of 3 m/s. What is its momentum?

• 45 kg·m/s

• 5 kg·m/s

• 18 kg·m/s

• -12 kg·m/s

Answer explanation

$p=m\cdot v$
$p=15\cdot3=45$ kg m/s

Tags

NGSS.HS-PS2-2

A 22 kg object has a velocity of 0.50 m/s. What is its momentum?

• 11 kg·m/s

• 44 kg·m/s

• 22.50 kg·m/s

• 4.4 kg·m/s

Answer explanation

$p=m\cdot v$

$p=22\cdot0.5=11$ kg m/s

Tags

NGSS.HS-PS2-2

A 6 kg ball slows from a velocity of 18 m/s to 12 m/s. What is its change in momentum?

• -36 kg·m/s

• 36 kg·m/s

• 1 kg·m/s

• -6 kg·m/s

Answer explanation

Remember that whenever you want to calculate a change, you calculate the final value minus the initial value.

$\Delta p=m\cdot\Delta v$
$\Delta v=12-18=-6$
$\Delta p=6\cdot\left(-6\right)=-36$ kg m/s

Tags

NGSS.HS-PS2-2

A 12 kg cart speeds up from rest to 8 m/s. What is its impulse?

• -4 kg·m/s

• 4 kg·m/s

• 48 kg·m/s

• 96 kg·m/s

Answer explanation

Remember that when you see the word "rest" in a problem about velocity, that means v = 0.

$J=\Delta p=m\cdot\Delta v$
$J=12\cdot\left(8-0\right)=12\cdot8=96$ kg m/s

Tags

NGSS.HS-PS2-2

What is the impulse when a 10 N force is applied for 3.5 s?

• 2.86 N·s

• 35 N·s

• 13.5 N·s

• -6.5 N·s

Answer explanation

$J=F\cdot t$

$J=10\cdot3.5=35$ kg m/s

Tags

NGSS.HS-PS2-1

How many seconds does it take for a force of 4.5 N to create a change in momentum of 36.9 kg·m/s?

• Not enough information to solve the problem.

• 8.2 s

• 32.4 s

• 166.05 s

Answer explanation

Since impulse creates change in momentum we can say this:

$J=\Delta p$
or
$F\cdot t=\Delta p$
$4.5\cdot t=36.9$
divide both sides by 4.5 to get the answer of 8.2

Tags

NGSS.HS-PS2-1