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MCAT Sample Questions ›› Physical Sciences

# MCAT Sample Questions : Physical Sciences

1. How much work is done when a constant horizontal 20-N force pushes a 50-kg block a distance of 10 m on a horizontal surface?

1. 50 J
2. 100 J
3. 200 J
4. 500 J

Explanation: Work is the product of the force on an object and the distance the object moves in the direction of the applied force. In this case, work = 20 N x 10 m = 200 J. Thus, answer choice C is the best answer.

2. Evaporation occurs when molecules at the surface of a liquid overcome the attractive forces of the liquid.This occurs when molecules within the liquid attain a sufficient amount of:

1. resonance.
2. kinetic energy.
3. surface tension.
4. potential energy.

Explanation: Evaporation occurs when a molecule attains sufficient speed or kinetic energy to overcome the attractive forces of a liquid. Resonance, surface tension and potential energy all relate to molecules that are not in motion. Thus, answer choice B is the best answer.

3. How long will it take a runner, starting from rest and accelerating uniformly at 1.5 m/s2, to travel 3.0 m?

1. 21/2 sec
2. 1.5 sec
3. 2.0 sec
4. 3.0 sec

Explanation: The relation between distance, acceleration, and time is: d = (1/2)a · t2. To solve for the time it takes the runner to use t = (2d/a)1/2 = (2×3/1.5)1/2 = 2 s. Therefore, answer choice C is the best answer.

4. A rectangular sheet of material has a width of 3 m and a length of 4 m.Forces with magnitudes of 3 N and 4 N, respectively, are applied parallel to two edges of the sheet, as shown in the figure below.

A third force, F, is applied to the center of the sheet, along a line in the plane of the sheet, at an angle ? = arctan 0.75 with respect to the horizontal direction.The sheet will be in translational equilibrium when F has what value?

1. F = 3 N
2. F = 4 N
3. F = 5 N
4. F = 7 N

Explanation: A body is in transitional equilibrium when the components of all external forces cancel. For the sheet: F cos ? = 4 N, F sin? = 3 N. The magnitude of F is found by adding the squares of the components: F2cos2 ? + F2 sin2 ?= F2 = 42 + 32 = 25 N2. Therefore F = 5 N. The F vector points in the proper direction since tan ? = 0.75 = 3/4. Thus, answer choice C is the best answer.

5. Which one of the following general characteristics is shared by all catalysts?

1. They induce more collisions among reactant molecules.
2. They transfer kinetic energy to the reactant molecules.
3. They increase the reaction rate but do not change the Keq of a reversible reaction.
4. They increase both the reaction rate and the Keq of a reversible reaction.

Explanation: In general, catalysts lower the activation energy of the slowest step in a reaction. Thus, they increase the rate of the reaction without increasing the number of collisions, the kinetic energy of the reactants, or the Keq of a reversible reaction. Thus, answer choice C is the best answer.

6. Radium, 226Ra, spontaneously decays to radon with the emission of an a-particle and a ? ray. If the speed of the a particle upon emission from an initially stationary radium nucleus is 1.5 x 107 m/s, what is the recoil speed of the resultant radon nucleus? Assume the momentum of the ? ray is negligible compared to that of the a particle.

1. 2.0 x 105 m/s
2. 2.7 x 105 m/s
3. 3.5 x 105 m/s
4. 1.5 x 107 m/s

Explanation: Conservation of linear momentum requires: mradonvradon= mheliumvhelium with helium identified as the alpha particle. The nuclear masses can be approximated by their mass numbers (222 and 4). Thus, the recoil speed of the radon is (4/222)×1.5 x 107 m/s = 2.7 x 105 m/s. Therefore, answer choice B is the best answer.

7. An object is placed upright on the axis of a thin convex lens at a distance of four focal lengths (4 f) from the center of the lens. An inverted image appears at a distance of 4/3 f on the other side of the lens. What is the ratio of the height of the image to the height of the object?

1. 1/3
2. 3/4
3. 4/3
4. 3/1

Explanation: The ratio of object to image distance equals the ratio of object to image height. The ratio of image to object height is found by rearranging the ratios to give 4f /(4/3)f = 1/3. The image is demagnified by a factor of 3. Thus, answer choice A is the best answer.

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