Twenty students ride a school bus that has a mass of 2500 kg and moves with a speed of 4.25 meters per second. The driver has a mass of 75 kg. What...

Momentum is the product of mass and velocity of a system. The total mass of the system includes the mass of the bus, mass of twenty students and the mass of driver.

Total mass = 2500 + 20 x 125 + 75 = 5,075 kg

speed of the bus = 4.25 m/sec

Momentum of the moving bus system = total mass x speed 

 = 5075 kg x 4.25 m/sec = 21,568.75 kg m/sec

If 8 students get off the bus, the mass of the moving bus system reduces. To maintain the same momentum, the speed of the bus will have to be increased.

The new mass of the system = 2500 + (20-8) x 125 + 75 = 4,075 kg

New speed of the bus = original momentum/new mass 

= 21,568.75/4075 m/sec = 5.29 m/sec.

Hope this helps.