## yrelhan4 2 years ago A truck is moving with a uniform velocity of 10 m/s.A leak occurs in the water tank of the truck at the rate of 2 kg/s.What is the speed of the truck after 50 seconds if the mass of the truck was 100 kg and mass of water in the tank initially was 100 kg?

1. Mashy

can you tell me what would be the mass of the truck after 5o seconds??

2. yrelhan4

100kgs.. all of sand will leak. right?

3. yrelhan4

water i am sorry..

4. eSpeX

Yes, you are losing 2kg/s so in 50 seconds you will lose 2kg/sec * 50sec = 100kg

5. armanfantasy

I dont no if it can be solved because there is two variable P(momentum) and v(velocity) in the equation

6. eSpeX

Well, since the problem gives the truck as moving with a uniform velocity, you know that it is not accelerating, meaning that it is not speeding up or slowing down. So after 50 seconds its momentum has changed but by definition its velocity has not.

7. armanfantasy

so the velocity is the same 10m/s but the momentum will be 1000 Ns

8. eSpeX

That is how I read the question, yes.

9. yrelhan4

but the asnwer given is 15m/s ..

10. yrelhan4

@eSpex also the velcoty cannot be 10m/s. since no external force is acting on the system conservation of momentum has to stand. i think the question is wrongly drafted.

11. Mashy

NO.. THE QUESTION is right.. use conservation of momentum!! initial mass = 200kg and initial velocity = 10m/s hence initial momentum = 2000kgm/s final mass = 100kg and final velocity = v .. but final momentum = 2000kgm/s itself hence 100v = 2000 or v = 20m/s!

12. Mashy

but when the water leaks the leaking water also has some momentum.. so in that case i really dunno how to solve the problem !

13. yrelhan4

@mashy will the system accelerate?

14. Mashy

it depends..i mean for example when the water leaks.. if i said that since the water has its inertia.. after it is seperated from the truck it continues to move along with the truck at same speed.. then the velocity wouldn't change!!.. and truck wouldn't accelerate

15. yrelhan4

the word uniform velocity in the sumin the first line is before the leak occurs, right?