# Homework Help: Newtons 2nd Law Problems

1. Oct 7, 2006

### soulja101

I really need help with this question. Ive tried solving it but i just cant do it.

The question

A loaded dump-truck having a total mass of 2.4*10power of 4 kg is travelling east at 85km/h.The truck driver can apply a braking force of 5.5*10 power of 4 to the wheels without causing the wheels to lock and skid. Calulate:
A)the maxium negative acceleration of this trunk.(in m/s2)
B)the minimum stopping time
C)the minimum stopping distance

The only thing I know is the mass. I know you are supposed to use the 85km/h for something I can not figure out for what.
Thanks

2. Oct 7, 2006

### Chi Meson

A) Newtons 2nd Law. What is it? As the truck brakes, what is the only unbalanced force on it?

3. Oct 7, 2006

### Astronuc

Staff Emeritus
Well, one has a mass 24000 kg, and a braking force of 55000 N (I guess N) based on the problem.

a) Apply F = ma, or a = F/m.

b) From a and the initial velocity, 85km/h (convert to m/s) compute the time that it takes for the truck to decelerate to v = 0 m/s.

c) From a and the initial velocity, compute the distance for the truck to decelerate to v = 0 m/s.

http://hyperphysics.phy-astr.gsu.edu/hbase/mot.html#mot1

http://hyperphysics.phy-astr.gsu.edu/hbase/newt.html#ntcon

4. Oct 7, 2006

### soulja101

what is 85km/h

what does 85km/h stand for and what do I use it for

5. Oct 8, 2006

### chroot

Staff Emeritus
85 kilometers per hour, I'd venture.

- Warren

6. Oct 8, 2006

### teknodude

That's your initial velocity and you have to do something with the units. Refer to the link Astronuc put up for the constant acceleration equations.

7. Oct 9, 2006

### soulja101

Thanks

Thanks so much for the help i tried your methods and they seem to work.