1) A mathematical pendulum , length L= 0.61 m oscillates in a uniformly accelerating vehicle. The acceleration is horizontal and equal to 3.2 m/ s^2 The period of oscillations is?(adsbygoogle = window.adsbygoogle || []).push({});

I don't know where to put in the acceleration when it is horizontal. I thought that if I just added the two vectorsmgandmaI would get the answer but that turned out to be the same as if I was moving up vertically..

2) At what speed v should an object move with respect to a system S in order that its density measured from S is n=1.088 times greater then its proper density ( i.e. density measured in a system in which object is at rest ). Express your result as a ratio v/c .

I got it so that: 1.088(RestDensity) = (RestDensity) / [ 1 - (v/c)^2 ]

After working it out I got my answer to be 0.284... but the "right" answer is 0.878.. that doesn't make any sense to me since you'd have to move at almost 90% the speed of light just to increase 1.088 times your rest density??

3) Calculate the speed at which the kinetic energy of a particle is equal to its rest energy. Express your result as v/c

This.. I got it to be 0.84 and the "right" answer is 0.87..

I used E^2 = p^2 * c^2 + m^2*c^4; where m is the rest mass and p is the momentum

equated p^2*c^2 to m^2*c^4 and solved for v by subbing p = mv where the m in this case is the relativisic mass. Is that just plain wrong?

Much thanks to anyone who can help, I've been at these problems for a while.. :<

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# Homework Help: Pendulum's and special relativity

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