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PHY 131–002 Oakton Community College Fall 2012 Practice Test 2 Useful formulas: v x t a v t A A Ax 2 Ay 2 Az 2 A Ax xˆ A y yˆ Az zˆ Constant acceleration: vx = v0x + axt x x 0 v 0 x t 12 a x t 2 Relative motion: rP|E rP|A rA|E v P|E v P|A v A|E Fnet ma w = mg a rad Ffriction = µFnormal v2 R Fg Gm1m2 r Fspring = –kx PEgrav = mgh PEspring vx2 = v0x2 + 2ax(x – x0) g = 9.80 m/s2 KE 1 2 kx 2 1 mv 2 2 P m r m rCM i RE 2 W t p Fnet t p mv Elastic collisions: vA – vB = v’B – v’A i i Gm E W = KE2 – KE1 KE1 + PEgrav, 1 + PEspring, 1 = KE2 + PEgrav, 2 + PEspring, 2 + heat mAvA + mBvB = mAv’A + mBv’B g G = 6.673 × 10–11 Nm2/kg2 2 W = Fd Ay 180 Ax arctan P Fext Ma CM t Mv CM P 100 cm = 1 m 1 km = 1000 m i i Conversion factors: 1 m = 109 nm 1 g/cm3 = 1000 kg/m3 1 m3 = 1000 L = 106 cm3 1 Pa = 1 N/m2 2 rad = 360° rad = 180° The Sun: mS = 1.99 × 1030 kg The Earth: mE = 5.97 × 1024 kg RE = 6.38 × 106 m rE = 1.50 × 1011 m 1 of 6 PHY 131–002 Oakton Community College Fall 2012 Practice Test 2 1) A net force Fnet 5.00 xˆ 12.00 yˆ acts on a 2.60 kg object at its center of mass. What is the magnitude of the object's acceleration? 2) Your nephew like pushing his 5.0 kg toy box around on the living room floor. He uses a constant force of 9.5 N directed 20° below the horizontal to push it along the floor at a constant velocity. What is the coefficient of kinetic friction, k, between the toy box and the living room carpet? (Assume there is no rotational component of motion.) 2 of 6 PHY 131–002 Oakton Community College Fall 2012 Practice Test 2 3) A person pushes a 35.0 kg box up a ramp that has an angle of 30° above horizontal. He uses a constant force of 235 N that is parallel to the ramp, and the velocity of the box is constant. What is the magnitude of the friction force between the box and the ramp? (Assume there is no rotational component of motion.) 4) An electron, whose mass is 9.11 × 10–31 kg, has a constant speed of 1.00 × 108 m/s. A magnetic field causes the electron to travel in a circular path of radius 1.00 cm without losing any speed. What is the magnitude of the force that the magnetic field exerts on the electron? 3 of 6 PHY 131–002 Oakton Community College Fall 2012 Practice Test 2 5) Conical pendulum: A pendulum made by placing a 0.250 kg ball at the end of a 1.00m massless cord swings in a conical path. The ball traces out a circle in a horizontal plane while maintaining the same height. If the cord maintains a 30° angle with the vertical, what is the speed of the ball? 6) Given that the radius of mars is 0.533 times that of earth, and its mass is 0.108 times that of earth: a) How much would a person weigh on mars if that person weighs 800.0 N on earth? b) If you could change the radius of mars without changing its mass, what radius would it have to have for this person's weight on mars to be the same as it is on earth? 4 of 6 PHY 131–002 Oakton Community College Fall 2012 Practice Test 2 7) A factory worker pushes a crate of mass 40.0 kg across the floor a distance of 10.0 m at a constant velocity using a horizontal force of 75.0 N. a) How much work is done on the crate by the worker? b) How much work is done on the crate by the floor? 8) A car on a frictionless horizontal track has a mass of 0.250 kg. It is connected to a spring and held at a position where the spring is compressed by 0.100 m. The force constant of the spring is 6.25 N/m. Assuming there is no friction, what is the speed of the car when the spring is at its uncompressed length (x = 0.0 m)? 5 of 6 PHY 131–002 Oakton Community College Fall 2012 Practice Test 2 9) A ball of mass 0.40 kg moves horizontally at a velocity of 25.0 m/s. It bounces off of a wall and it has a velocity of 18.0 m/s in the opposite direction. The ball was in contact with the wall for 0.015 s. What was the average force exerted on the ball by the wall? 10) On a frictionless track, car A, with mass mA = 0.300 kg, moves to the right toward car B with velocity vA = +2.00 m/s. Car B, with mass mB = 0.250 kg, moves toward car A with a velocity of vB = –1.50 m/s. After the collision, car B has a velocity of v’B = +1.50 m/s. a) What is the velocity of car A after the collision, v’A? b) What is the change in the kinetic energy of this two-car system? 6 of 6