# Question #30dd4

##### 2 Answers

#### Explanation:

The formula for momentum is

Now we have to convert 72km/h into m/s:

Now calculate initial momentum:

When the ball returns, the velocity

So

But if we consider that initial velocity is negative we get the answer that is additive inverse of what we got earlier , that's +8 .

Actually the momemtum hasn't changed just its direction reversed . So , there's an addition of a '-' ve sign .

#### Explanation:

The formula for momentum is

#color(blue)(sf( momentum=massxxvelocity#

Where, the mass is expressed in kilograms and the velocity is expressed in

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We need to convert our known values in the coventional units

#color(brown)(200g=#

Since,

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

#color(brown)(72(km)/h=#

Since,

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Now, calculate momentum

We need to find the change in momentum

#color(violet)(sf"change in momentum"="Final momentum"- "Initial momentum"#

Since, the ball returns with the same momentum and in the opposite direction,

Hope that that helps!!! ☺♦☻