Question

A girl of mass 30 kg jumps on a cart of mass 5 kg with a velocity of 10 m/s2. Find the velocity with which she and cart start moving after she jumps on it?
Please answer as fast as you can, it's very urgent.....

Answer 1

We know that,

momentum before collision = momentum after collision

So total momentum before collision = momentum of girl + momentum of cart

= 30 × 10 + 5 × 0

(since, momentum = mass × velocity)

= 300 kg m/s

Now, let the velocity of cart after collision be v

So, momentum after collision = (30 + 5) × v

(since, the girl will stand on cart, the total mass = mass of girl + mass of cart)

= 35v kg m/s

So, momentum before collision = momentum after collision

=> 300 = 35v

=> v = 300/35

=> v = 60/7 m/s

or, v = 8.57 m/s (approx)

Answer :- 60/7 m/s or 8.57 m/s (approx)

Answer 2

We know,

Momentum remains conserved,

So,

Momentum before collision = girl + cart

= m*v + m'*v'

= 30*10 + 5*0

= 300 kg m/s

According to the question,

Momentum after collision = (30+5)*v"

= 35*v" kg m/s

Now,

Equating the momentum before and after,

35*v" = 300

v" = 300/35

= 8.571 m/s (approx)

So the final velocity = 8.571 m/s

Hope this helps you out!