A projectile of mass `50 kg` is shot vertically upwards with an initial velocity of `100 m//s`. After `5 s`, it explodes into two fragments, one of which having a mass of `20 kg` travels vertically up with a velocity of `150 m//s`:
a. What is the velocity of the other fragment that instant?
b. Calculate the sum of momentum of fragment `3s` after the explosion. What would have been the momentum of the projectile at this instant if there had hem explosion?

Explanation

### Step-by-Step Solution

**Given Data:**
- Mass of projectile, \( m = 50 \, \text{kg} \)
- Initial velocity, \( u = 100 \, \text{m/s} \)
- Time before explosion, \( t = 5 \, \text{s} \)
- Mass of fragment 1, \( m_1 = 20 \, \text{kg} \)
- Velocity of fragment 1 after explosion, \( v_1 = 150 \, \text{m/s} \)
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