# Homework Help: Dynamics of material (momentum )

1. Mar 18, 2016

### Faraz

< Mentor Note -- thread moved to HH from the technical physics forums, so no HH Template is shown >

Hi, Im having difficulty solving the problem, please resolve it if possible. my work and the image for the problem is attached. Thanks
The 10 kg block is at rest on the bottom of the incline (θ = 30°) when it is suddenly struck by a 50 kN force that sends it sliding up the incline. The duration of the force is 5 ms and the coefficient of kinetic friction between the block and the incline is 0.2. The block slides 30 m up the incline and makes contact with the spring (initially uncompressed, k = 15 kN/m). What is the maximum compression of the spring

Last edited by a moderator: Mar 18, 2016
2. Mar 19, 2016

### ehild

You solved a different problem. What does the 50 kN force do with the 10 kg block in 5 ms?

3. Mar 19, 2016

### Faraz

i KNOW i should use conservation of momentum but dont know how

4. Mar 19, 2016

### ehild

Momentum is conserved if no force acts on the body.
There are forces acting on the 10 kg block. It is in rest initially. Does it stay in rest when the force acts on it ?

5. Mar 19, 2016

### Faraz

no

6. Mar 19, 2016

### Faraz

so why is the time given

7. Mar 19, 2016

### Faraz

im really confused, cuz in that case my solution is correct

8. Mar 19, 2016

### ehild

Will it move? with what velocity?

9. Mar 19, 2016

### ehild

In what case?

10. Mar 19, 2016

### Faraz

did you check out the attachments?

11. Mar 19, 2016

### ehild

Yes. It is wrong. You did not you use the given force and time, what you did is not related to the problem.

12. Mar 19, 2016

### Faraz

ive done it numerous times, can you actually help me solve it

13. Mar 19, 2016

### ehild

I tried to help you, but you said that you solved the problem correctly.
I ask again: what happens to a body if force is applied to it?

14. Mar 19, 2016

### Faraz

it moves

15. Mar 19, 2016

### ehild

Imagine the setup. There is a block in rest at the bottom of a slope. Far away from it, there is a spring at the top of the slope. How can the block compress the spring? It has to reach it. For that , it needs enough velocity. How does it get velocity? If force is applied to it.
It accelerates, gains some velocity and momentum during some time.
How is the change of momentum related to the force and time of application of the force?

Last edited: Mar 19, 2016
16. Mar 19, 2016

### Faraz

impulse?

17. Mar 19, 2016

### ehild

Yes, impulse. What impulse does the block get if 50 kN force is applied for 5ms?

18. Mar 19, 2016

### Faraz

ft

19. Mar 19, 2016

### ehild

How much is it? and what velocity does the block gain from that impulse?

20. Mar 19, 2016

### Faraz

21. Mar 19, 2016

### Faraz

i just resolved it, is it correct?

22. Mar 19, 2016