Kevin S. Huang

  • F=ma Exam Solutions

    Please find my solutions to past F=ma Contest problems below. Past Exams Problems organized by topic Quarter-final Exams Problems organized by topic

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  • 2007: Problem 8

    Topic: GravityConcepts: Gravitational potential energy Solution: Recall the gravitational potential energy between two masses is given by under the standard convention that U→0U \rightarrow 0 as r→∞r \rightarrow \infty. We have Thus, so the answer is B.

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  • 2007: Problem 7

    Topic: EnergyConcepts: Kinetic energy Solution: The energy required to go from 0mph0 \,\mathrm{mph} to 2mph2 \,\mathrm{mph} is The energy required to go from 2mph2 \,\mathrm{mph} to 4mph4 \,\mathrm{mph} is Thus, so the answer is D.

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  • 2007: Problem 6

    Topic: KinematicsConcepts: General kinematics equations Solution: Recall velocity is defined by so We have v=5t2v=5t^2 and x0=0x_0=0: Hence, so the answer is B.

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  • 2007: Problem 5

    Topic: DynamicsConcepts: Forces in mechanics Solution: Consider the forces acting on the crate: Only static friction is directed up along the hill and increases the speed of the crate. Thus, the answer is A.

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  • 2007: Problem 4

    Topic: KinematicsConcepts: Free fall Solution: Recall one of our kinematics equations for uniform acceleration: For dropping an object from rest, we have v0=0v_0=0 and a=ga=g: In the first unit of time, In the total two units of time, Hence, the object fell during the second unit of time so the answer is C.

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  • 2007: Problem 3

    Topic: KinematicsConcepts: Average vs. instantaneous Solution: We have The average velocity is defined as so the answer is B.

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  • 2007: Problem 2

    Topic: KinematicsConcepts: Motion graphs Solution: From kinematics, so acceleration corresponds to the slope on a v-t plot. The slope at t=90st=90 \,\mathrm{s} is so the answer is B.

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  • 2007: Problem 1

    Topic: KinematicsConcepts: Vectors Solution: The equation of the x-axis is given by y=0y=0. Hence, the particle crosses the x-axis when so the answer is E.

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  • K1

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1D elastic collision 1D inelastic collision 5 kinematics equations Air resistance Angular kinematics Angular momentum Artificial gravity Atwood machine Average vs. instantaneous Ballistic pendulum Bernoulli's principle Block on conveyor belt Buoyant force Center of mass Circular motion Circular orbits CM frame Conservation of angular momentum Conservation of energy Conservation of linear momentum Coriolis force Data expression Dimensional analysis Dynamics Dynamics of CM Effective spring constant Elliptical orbits Energy dissipation Equivalence principle Error propagation Escape velocity Fictitious forces Floating Fma: Collisions Fma: Dynamics Fma: Energy Fma: Fluids Fma: Gravity Fma: Kinematics Fma: Oscillatory Motion Fma: Other Fma: Rigid Bodies Fma: System of Masses Forces in mechanics Free fall Gauss's law for gravity General angular momentum General kinematics equations General kinetic energy General Newton's 2nd law Gravitational force Gravitational potential energy Impulse-momentum theorem Inclined plane Kepler's laws Kinematics Kinetic energy Law of reflection Limiting cases Mass-spring system Mechanics Moments of inertia Motion graphs Newton's laws Parallel-axis theorem Pascal's law Perpendicular-axis theorem Physical pendulum Potential energy graphs Power Pressure with depth Projectile motion Pulleys with rotational inertia Qtrfin: E&M Qtrfin: Mechanics Reduced mass Relative velocity Rigid Bodies Rolling down inclined plane Rolling motion Rotational Newton's 2nd law Scale reading Simple harmonic motion Simple pendulum Small angle approximation Speed vs. velocity Spring potential energy Statics Surface tension Tensile strength Torque Torque from weight Types of equilibrium Vectors Velocity constraints Vertical spring Wave speed in string Work Work-energy theorem Young's modulus