# Physics question from TPR

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#### goodYvening

##### Full Member

Consider a quadruped of roughly the same mass and proportion as the human above (say, a large cat), with roughly the same time of contact of the foot with the ground and the same force exerted in the running limbs. Which of the following is true of bipeds and quadrupeds maintaining a steady run?

A)
The biped expends more energy in producing upward motion.

B)
The quadruped expends more energy in producing upward motion.

C)
The biped must use either more force or more time to bring limbs into position to break a fall.

D)
The biped exerts a greater force during the thrusting portion of the run.

#### depasqualemi

##### New Member
5+ Year Member
If I were to answer this I'd put C. I don't know if I'm correct though. My reasoning is that the question addresses the fact that both the biped and quadruped are of equal mass, and because Kinetic energy is a function of mass and velocity (which both are held constant) A and B must be false. Force is also a function of mass, as well as acceleration (both again, held constant) so D must be false. What is the correct answer?

#### goodYvening

##### Full Member
You are correct, the answer is C. I know the question says they maintain a stead run, but it does not say they maintain the same velocity. How did you know/were able to assume that?

#### depasqualemi

##### New Member
5+ Year Member
They're asking about force and kinetic energy, so from there I think, "ok what is the formula for KE and F". I do this because these variables are dependent on multiple factors, including velocity for both. However, the question never addresses velocity, so I know that isn't an important factor to determining my answer, so I assumed both move at the same speed. KE doesn't determine how fast you move, it's how fast you move that determines KE.

#### ThePrincetonReview

##### Test Prep Exhibitor
Vendor
10+ Year Member
7+ Year Member

Consider a quadruped of roughly the same mass and proportion as the human above (say, a large cat), with roughly the same time of contact of the foot with the ground and the same force exerted in the running limbs. Which of the following is true of bipeds and quadrupeds maintaining a steady run?

A)
The biped expends more energy in producing upward motion.

B)
The quadruped expends more energy in producing upward motion.

C)
The biped must use either more force or more time to bring limbs into position to break a fall.

D)
The biped exerts a greater force during the thrusting portion of the run.