There’s a lot happening at the start of an Olympic BMX race. Athletes begin at the top of a ramp, which they descend while pedaling and being pulled by gravity. At the end of the ramp, they transition from pointing down to aiming horizontally. You may not think there are many physics problems here, but there are.
How fast would you go if you didn’t pedal?
One claim about Olympic BMX is that the riders descend the ramp in twoseconds ata velocity of about 35 mph( 15.6 m/ s ). What if you simplyrolled down the incline and let gravitation accelerate you? How fast would you be going? Of course, this question are dependent upon the extent of the ramp. An official begin ramp has a height of 8 meters with dimensions something like this( they aren’t altogether straight ).
Instead of a bike, I’ve placed a frictionless block at the opening of the ramp. If I want to determinethe speed of this sliding block at the bottom of the ramp, I can start with one of several principles. However, the Work-Energy Principle is more straightforward approach. This statesthat the work done on a system is equal to the altered in energy.
If I viewthe block and the Earth as the organizations of the system, the only external force-out isthe force from the ramp. Such a force always pushes perpendicular to the direction the block moves such that the total work on the organizations of the system is zero. That leaves a total change in energy of zero Joules. In this case, there are two types of energy–kinetic energy and gravitational potential energy.
There are two important points about gravitational potential energy 😛 TAGEND The value of y doesn’t really matter. Since the Work-Energy Principle only deals with the change in gravitational potential energy, Ionly care about the change in y. For this situation, I will use the bottom of the ramp as my y= 0 meters( but you could put this anywhere ). Again, the altered in potential only depends on the change in height. It does not depend on how far the block moves horizontally. This means that the slant of the ramp doesn’t really change the final velocity of the block( but only in the case where friction doesn’t matter ). Toni Syarifudin of Indonesia vies in the Cycling- BMX Men’s Seeding Run at The Olympic BMX Centre on August 17, 2016. Christian Petersen/ Getty Images g c