MCAT Physics Question — Ice Skaters
 by
 May 26, 2014
 MCAT Blog, MCAT Physics, MCAT Question of the Day
A motionless, inexperienced ice skater of 70kg faces forward with skates parallel. A more experienced skater of 80kg collides with the stationary skater at a speed of 2m/sec.Both skaters move off together with the same velocity. If ice is considered frictionless, what is the approximate speed of the two skaters after the collision?
a) 1.1m/sec
b) 1.4 m/sec
c) 2 m/sec
d) 4 m/sec
Explanation
When two masses collide and move with the same velocity after impact, conservation of momentum must be applied. m_{1}v_{1}+m_{2}v_{2}=(m_{1}+m_{2})v_{final}, where v_{1}and v_{2} are the initial velocities of masses 1 and 2. Here, skater 1 has mass of 70kg and initial velocity of 0m/sec. Skater 2 has a mass of 80kg and initial velocity of 2m/sec.
Applying conservation of momentum, v_{final}=m_{2}/( m_{1}+m_{2})*v_{2}. From looking at the numbers, v_{final} is approximately 1/2 of v_{2} because the skaters have roughly the same mass. Choice a is correct.
a) 1.1m/sec, correct.
b) 1.4 m/sec, incorrect, This assumes kinetic energy before and after is equal. Energy is not conserved in an inelastic collision.
c) 2 m/sec, incorrect, This assumes that speed stays constant after a collision.
d) 4 m/sec, incorrect, This is the initial velocity of the experienced skater squared.
Want more MCAT practice?
We’ve got options for every schedule and learning style!
From the best online MCAT course created by top instructors with 524+ MCAT scores to the most representative fulllength practice exams and private tutoring, we can custom tailor your MCAT prep to your goals!
Not sure which option is right for you? Schedule a free MCAT consultation with an MCAT Advisor using the form below. No obligation, just expert advice.
Search the Blog
Free Consultation
Interested in our Online MCAT Course, OneonOne MCAT Tutoring or Med admissions packages? Set up a free consultation with one of our experienced Senior Student Advisors.
Schedule NowPopular Posts

MCAT Blog How to Review MCAT FullLengths
Free MCAT Practice Account
Need great MCAT practice?Get the most representative MCAT practice possible when you sign up for our free MCAT Account, which includes a halflength diagnostic exam and one of our fulllength MCAT practice exams.
Learn More
Submit a Comment