# Stuck on three physics tasks (momentum, force)

Printable View

• October 20th 2012, 08:36 AM
Glyper
Stuck on three physics tasks (momentum, force)
Could you please help me with these three tasks?

1. A trolley weighing 16 000kg is moving along a horizontal surface with a velocity od 6m/s. What braking force would cause it to brake on a distance of 10m and how long it would take?
2. A cycler is going through the winding, cycling on a circle of radius 6m and is slanting with alpha=75^ to the horizontal surface. What's his velocity?
3. A body of small dimensions is sliding from an apex of a sphere of radius R down. At what height h from the apex the body will lose contact from the sphere? (assume the friction is low)

My thoghts:

1. a = F/m = ΔV/t. So ΔV = 6m/s, m=16 000kg, s = 10m and F = mΔV/Δt. We know neither F nor t so how could I solve this? It's just one equation but two unknown variables.
2. We have two forces on the cycler - centrifugal force and friction. They are equal (or at least should be? Though I don't know why...) so we have T=Fc and thus $\frac{mv^{2}}{R}=\mu F_{N}$. How should I use it, though, if I have only 75^ and the radius given?
3. Oh my, been cracking my head over it for some time and know not even where to start...

Could you please hlp me understand?
• October 22nd 2012, 05:24 AM
Krahl
Re: Stuck on three physics tasks (momentum, force)
1.

m = 16,000kg
v = 6m/s
S = 10m

The velocity equation is $v = at+v_0$
The distance equation is $S = \frac{1}{2}at^2+v_0 t$

Try and use those two equations along with the information you've been given to solve for both $a$ and $t$