Physics Exam 2

A bat strikes a 0.050-kg baseball so that its velocity changes by +30 m/s in 0.10 s. With what average force was the ball struck? (a) +15 N (c) +300 N (e) +150 N (b) 15 N (d) 300 N

(a) +15 N

A 50.0-kg boy runs at a speed of 10.0 m/s and jumps onto a cart as shown in the figure. The cart is initially at rest. If the speed of the cart with the boy on it is 2.50 m/s, what is the mass of the cart? (a) 150 kg (c) 210 kg (e) 300 kg (b) 175 kg (d) 260 kg

(a) 150 kg

A 2.00-kg projectile is fired at an angle of 20.0°. What is the magnitude of the force exerted on the projectile when it is at the highest position in its trajectory? Neglect any effects of air resistance. (a) 19.6 N (c) 9.80 N (e) 0 N (b) 14.7 N (d) 4.90 N

(a) 19.6 N

A concrete block is pulled 7.0 m across a frictionless surface by means of a rope. The tension in the rope is 40 N; and the net work done on the block is 247 J. What angle does the rope make with the horizontal? (a) 28° (c) 47° (e) 88° (b) 41° (d) 62°

(a) 28°

A 1500-kg SUV travels at a constant speed of 22 m/s around a circular track that has a radius of 85 m. What is the magnitude of the acceleration of the SUV? (a) 5.7 m/s2 (c) 9.8 m/s2 (e) zero m/s2 (b) 0.26 m/s2 (d) 1.2 m/s2

(a) 5.7 m/s2

A rock is thrown straight up from the earth's surface. Which one of the following statements concerning the net force acting on the rock at the top of its path is true? (a) The net force is equal to the weight of the rock. (b) The net force is instantaneously equal to zero newtons. (c) The net force's direction changes from up to down. (d) The net force is greater than the weight of the rock. (e) The net force is less than the weight of the rock, but greater than zero newtons.

(a) The net force is equal to the weight of the rock.

Complete the following statement: Different types of collisions between interacting bodies are categorized on the basis of (a) kinetic energy conservation. (d) the magnitude of the forces involved. (b) mechanical energy conservation. (e) the temporal duration of the collision. (c) linear momentum conservation.

(a) kinetic energy conservation

Complete the following statement: The maximum speed at which a car can safely negotiate a frictionless banked curve depends on all of the following except (a) the mass of the car. (b) the angle of banking. (c) the diameter of the curve. (d) the radius of the curve. (e) the acceleration due to gravity.

(a) the mass of the car.

A ball moves with a constant speed of 4 m/s around a circle of radius 0.25 m. What is the period of the motion? (a) 0.1 s (c) 0.7 s (e) 2 s (b) 0.4 s (d) 1 s

(b) 0.4 s

How much energy is dissipated in braking a 1000-kg car to a stop from an initial speed of 20 m/s? (a) 20 000 J (c) 400 000 J (e) 10 000 J (b) 200 000 J (d) 800 000 J

(b) 200 000 J

The orbital radius of Saturn about the Sun is about 10 times that of Earth. Complete the following statement: The period of Saturn is about (a) 10 yr. (c) 40 yr. (e) 160 yr. (b) 30 yr. (d) 90 yr.

(b) 30 yr

In which one of the following systems is there a decrease in gravitational potential energy? (a) a boy stretches a horizontal spring (d) a car ascends a steep hill (b) a girl jumps down from a bed (e) water is forced upward through a pipe (c) a crate rests at the bottom of an inclined plane

(b) a girl jumps down from a bed

During the construction of a high rise building, 40-kg block is vertically lifted 20 meters from the surface of the earth. To one significant figure, what is the change in the gravitational potential energy of the block? (a) +800 J (b) -800 J (c) +8000 J (d) -8000 J (e) zero joules

(c) +8000 J

A projectile is launched with 200 kg m/s of momentum and 1000 J of kinetic energy. What is the mass of the projectile? (a) 5 kg (c) 20 kg (e) 50 kg (b) 10 kg (d) 40 kg

(c) 20 kg

What is the weight of a 2.50-kg bag of sand on the surface of the earth? (a) 2.50 N (c) 24.5 N (e) 98.0 N (b) 9.80 N (d) 49.0 N

(c) 24.5

The kinetic energy of a car is 8 x10^6 J as it travels along a horizontal road. How much power is required to stop the car in 10 s? (a) zero watts (b) 8 x10^4 W (c) 8 x10^5 W (d) 8 x10^6 W (e) 8 x10^7 W

(c) 8 x10^5 W

A 2.0-kg object moves in a straight line on a horizontal frictionless surface. The graph shows the velocity of the object as a function of time. The various equal time intervals are labeled using Roman numerals: I, II, III, IV, and V. The net force on the object always acts along the line of motion of the object. Which section(s) of the graph correspond to a condition of zero net force? (a) V only (b) III only (c) II and IV (d) II, III, and IV (e) I, III, and V

(c) II and IV

A racecar is traveling at constant speed around a circular track. What happens to the centripetal acceleration of the car if the speed is doubled? (a) The centripetal acceleration remains the same. (b) The centripetal acceleration increases by a factor of 2. (c) The centripetal acceleration increases by a factor of 4. (d) The centripetal acceleration is decreased by a factor of one-half. (e) The centripetal acceleration is decreased by a factor of one-fourth

(c) The centripetal acceleration increases by a factor of 4.

An object of mass 3m, initially at rest, explodes breaking into two fragments of mass m and 2m, respectively. Which one of the following statements concerning the fragments after the explosion is true? (a) They will fly off at right angles. (b) They will fly off in the same direction. (c) The smaller fragment will have twice the speed of the larger fragment. (d) The larger fragment will have twice the speed of the smaller fragment. (e) The smaller fragment will have four times the speed of the larger fragment.

(c) The smaller fragment will have twice the speed of the larger fragment.

Which one of the following situations is an example of an object with a non-zero kinetic energy? (a) a drum of diesel fuel on a parked truck (d) a car parked at the top of a hill (b) a stationary pendulum (e) a boulder resting at the bottom of a cliff (c) a satellite in geosynchronous orbit

(c) a satellite in geosynchronous orbit

An apple crate with a weight of 225 N accelerates along a frictionless surface as the crate is pulled with a force of 14.5 N as shown in the drawing. What is the horizontal acceleration of the crate? (a) 1.40 m/s2 (c) 1.29 m/s2 (e) 0.644 m/s2 (b) 0.427 m/s2 (d) 0.597 m/s2

(d) 0.597 m/s2

In which one of the following situations is zero net work done? (a) A ball rolls down an inclined plane. (b) A physics student stretches a spring. (c) A projectile falls toward the surface of Earth. (d) A box is pulled across a rough floor at constant velocity. (e) A child pulls a wagon across a rough surface causing it to accelerate.

(d) A box is pulled across a rough floor at constant velocity.

An object moves due east at constant speed. A net force directed due north then acts on the object for 5.0 s. At the end of the 5.0-second period, the net force drops to zero newtons. Which one of the following statements is necessarily true? (a) The object will be moving eastward when the force drops to zero newtons. (b) The change in the velocity of the object will be directed north of west. (c) The direction of the object's acceleration depends on how fast the object was initially moving. (d) The final velocity of the object will be directed north of east. (e) The magnitude of the object's acceleration depends on how fast the object was initially moving.

(d) The final velocity of the object will be directed north of east.

A rock is thrown straight up from the surface of the Earth. Which one of the following statements describes the energy transformation of the rock as it rises? Neglect air resistance. (a) The total energy of the rock increases. (b) The kinetic energy increases and the potential energy decreases. (c) Both the potential energy and the total energy of the rock increase. (d) The kinetic energy decreases and the potential energy increases. (e) Both the kinetic energy and the potential energy of the rock remain the same.

(d) The kinetic energy decreases and the potential energy increases.

A boy is whirling a stone around his head by means of a string. The string makes one complete revolution every second; and the tension in the string is FT. The boy then speeds up the stone, keeping the radius of the circle unchanged, so that the string makes two complete revolutions every second. What happens to the tension in the sting? (a) The tension is unchanged. (b) The tension reduces to half of its original value. (c) The tension increases to twice its original value. (d) The tension increases to four times its original value. (e) The tension reduces to one-fourth of its original value.

(d) The tension increases to four times its original value.

Which one of the following is not a unit of energy? (a) foot /pound (b) kilowatt/ hour (c) newton/ meter (d) watt (e) joule

(d) watt

Which one of the following statements concerning momentum is true? (a) Momentum is a force. (b) Momentum is a scalar quantity. (c) The SI unit of momentum is kg m2/s. (d) The momentum of an object is always positive. (e) Momentum and impulse are measured in the same units.

(e) Momentum and impulse are measured in the same units.

The earth exerts the necessary centripetal force on an orbiting satellite to keep it moving in a circle at constant speed. Which one of the following statements best explains why the speed of the satellite does not change although there is a net force exerted on it? (a) The satellite is in equilibrium. (b) The acceleration of the satellite is zero m/s2. (c) The centripetal force has magnitude mv2/r. (d) The centripetal force is canceled by the reaction force. (e) The centripetal force is always perpendicular to the velocity.

(e) The centripetal force is always perpendicular to the velocity.

The figure shows the velocity versus time curve for a car traveling along a straight line. Which of the following statements is false? (a) No net force acts on the car during interval B. (b) Net forces act on the car during intervals A and C. (c) Opposing forces may be acting on the car during interval B. (d) Opposing forces may be acting on the car during interval C. (e) The magnitude of the net force acting during interval A is less than that during C.

(e) The magnitude of the net force acting during interval A is less than that during C.

A 70.0-kg astronaut pushes to the left on a spacecraft with a force F in "gravity-free" space. The spacecraft has a total mass of 1.0 104 kg. During the push, the astronaut accelerates to the right with an acceleration of 0.36 m/s2. 7. Which one of the following statements concerning this situation is true? (a) The spacecraft does not move, but the astronaut moves to the right with a constant speed. (b) The astronaut stops moving after he stops pushing on the spacecraft. (c) The force exerted on the astronaut is larger than the force exerted on the spacecraft. (d) The force exerted on the spacecraft is larger than the force exerted on the astronaut. (e) The velocity of the astronaut increases while he is pushing on the spacecraft.

(e) The velocity of the astronaut increases while he is pushing on the spacecraft.

Which one of the following statements concerning center of mass is true? (a) All of an object's mass is located at its center of mass. (b) The center of mass of an object must be located within the object. (c) The center of mass of a system of objects cannot change even if there are forces acting on the objects. (d) The velocity of the center of mass of a system of objects is greatly affected by a collision of objects within the system. (e) The velocity of the center of mass of a system of objects is constant when the sum of the external forces acting on the system is zero.

(e) The velocity of the center of mass of a system of objects is constant when the sum of the external forces acting on the system is zero.

Which force is responsible for holding a car in a frictionless banked curve? (a) the reaction force to the car's weight (b) the vertical component of the car's weight (c) the vertical component of the normal force (d) the horizontal component of the car's weight (e) the horizontal component of the normal force

(e) the horizontal component of the normal force

Work may be expressed using all of the following units except: (a) N /m (c) erg (e) watt (b) joule (d) ft / lb

(e) watt

Complete the following statement: An inertial reference frame is one in which (a) Newton's first law of motion is valid. (b) the inertias of objects within the frame are zero. (c) the frame is accelerating. (d) the acceleration due to gravity is greater than zero m/s2. (e) Newton's third law of motion is not valid.

a) Newton's first law of motion is valid.

With one exception, each of the following units can be used to express mass. What is the exception? a) newton b)slug c)gram d)Ns2/m e)kilogram

newton