Question

Example 9.7 A girl of mass 40 kg jumps
with a horizontal velocity of 5 ms? onto
a stationary cart with frictionless
wheels. The mass of the cart is 3 kg.
What is her velocity as the cart starts
moving? Assume that there is no
external unbalanced force working in
the horizontal direction.
Solution:​

Answer 1

no external force  =>  momentum is constant.

  momentum of girl = 40 * 5 = 200 kg-m/sec

 momentum of girl and cart = total momentum of the girl + momentum of cart

        = 200 + 0 = 200 kg m/sec

    speed     = 200 / (40 + 3)  

            = 4.65 m/sec

Answer 2

Answer:

Mass of the girl = 40 kg

Mass of the cart = 3 kg

Velocity of the girl = 5 m/s

Velocity of the cart = 0 m/s

To Find :-

Velocity as the cart starts moving.

Solution :-

Firstly let's find the Mounmentum of girl

[P = mv]

Here,

P = Mounmentum

M = Mass

V = Velocity

P = 40 × 5

Hence, Mounmentum of girl is 200 kg m/s .

Now,

Let's add the Mounmentum of girl and cart

200 + 0 = 200 kg m/s

Let's find total mass

Total mass = 40 + 3 = 43 kg

Velocity=Mounmentum/mass

V = P/M

Velocity = 200/43

Hence :-

Velocity of cart is when start moving is 4.65 m/s.

@ananya