Physics 101 Chapter 3

An archeologist is running at 4 m/s with her hands outstretched above her head (1.75 m from feet to fingertips) while being chased by a tiger. She runs exactly horizontally off of a chasm and attempts to grab onto the opposite side. (a) If the chasm is 4.90 meters wide, how long does she take to cover this distance? (b) During this time, what distance has she fallen vertically (use g = 10 m/s2)? (c) How far above or below the edge of the opposite side do her fingertips fall? (Use + to indicate distances above the edge and − to indicate distances below the edge.)

(a) 1.23 s (b) 7.5 m (c) -5.75 m

A ball is thrown upward with an initial velocity of 15 m/s. Using the approximate value of g = 10 m/s2, how high above the ground is the ball at the following times? (a) 1.10 s after it is thrown (b) 2.10 s after it is thrown

(a) 10.5 m (b) 9.45 m

A steel ball is dropped from a diving platform (with an initial velocity of zero). Use the approximate value of g = 10 m/s2. (a) What is the velocity of the ball 1.2 seconds after its release? (b) What is its velocity 3.3 seconds after its release?

(a) 12 m/s (b) 33 m/s

A steel ball is dropped from a diving platform (with an initial velocity of zero). Use the approximate value of g = 10 m/s2. (a) Through what distance does the ball fall in the first 1.7 seconds of its flight? (b) How far does it fall in the first 4 seconds of its flight?

(a) 14.45m (b) 80m

A ball is thrown upward with an initial velocity of 12 m/s. Using the approximate value of g = 10 m/s2, what are the magnitude and direction of the ball's velocity at the following times? (a) 0.90 s after it is thrown ___________m/s a. downward b. upward (b) 1.90 s after it is thrown ___________m/s a. downward b. upward

(a) 3 m/s; b. (b) 7 m/s; a.

(a) A ball rolls up an inclined plane, slows to a stop, and then rolls back down. Do you expect the acceleration to be constant during this process? a. Yes b. No (b) Is the velocity constant? a. Yes b. No (c) Is the acceleration equal to zero at any point during this motion? a. Yes b. No

(a) a. Yes (b) b. No (c) b. No

A ball rolls off a shelf with a horizontal velocity of 5 m/s. At what horizontal distance from the shelf does the ball land if it takes 0.5 s to reach the floor?

2.5 m

A lead ball and an aluminum ball, each 1 in. in diameter, are released simultaneously and allowed to fall to the ground. Due to its greater density, the lead ball has a substantially larger mass than the aluminum ball. Which of these balls, if either, has the greater acceleration due to gravity? Explain. a. Both will fall with the same acceleration, regardless of their mass. b. The lead ball will fall with greater acceleration because of its greater mass. c. The aluminum ball will fall with greater acceleration because of its small density.

a. Both will fall with the same acceleration, regardless of their mass.

Is it possible for an object to have a horizontal component of velocity that is constant at the same time that the object is accelerating in the vertical direction? a. Yes b. No

a. Yes

Will a shot fired from a cannon at a 20° angle travel a longer horizontal distance than a 45° shot? Explain. a. Yes, the cannonball fired at an angle of 20° has a larger horizontal component of velocity and will travel a longer horizontal distance than the cannonball fired at 45°. b. No, although the cannonball fired at an angle of 20° does have a larger horizontal component of velocity it does not stay in the air nearly as long as the cannonball fired at 45°. c. There is not enough information to determine which cannonball will travel a longer horizontal distance.

b. No, although the cannonball fired at an angle of 20° does have a larger horizontal component of velocity it does not stay in the air nearly as long as the cannonball fired at 45°.

A cannonball fired at an angle of 70° to the horizontal stays in the air longer than one fired at 45° from the same cannon. Will the 70° shot travel a greater horizontal distance than the 45° shot? Explain. a. Yes, since the cannonball fired at an angle of 70° stays in the air longer it will travel a greater horizontal distance than the cannonball fired at 45°. b. No, the cannonball fired at 70° has a larger vertical component of velocity so will have a higher ascent and will not travel as far horizontally as the cannonball fired at 45°. c. There is not enough information to determine which cannonball will travel a greater horizontal distance.

b. No, the cannonball fired at 70° has a larger vertical component of velocity so will have a higher ascent and will not travel as far horizontally as the cannonball fired at 45°.

A ball rolls off a table with a large horizontal velocity. Does the direction of the velocity vector change as the ball moves through the air? Explain. a. Yes, the velocity of the ball is in the x-direction while it rolls on the table and in the y-direction as it falls to the floor. b. Yes, although the horizontal component remains constant the vertical component increases downward, changing the resultant velocity vector. c. No, the velocity of the ball is constant in the x- and y-direction , so the direction of the velocity vector does not change.

b. Yes, although the horizontal component remains constant the vertical component increases downward, changing the resultant velocity vector.

A ball rolling rapidly along a tabletop rolls off the edge and falls to the floor. At the exact instant that the first ball rolls off the edge, a second ball is dropped from the same height. Which ball, if either, reaches the floor first? Explain. a. The rolling ball reaches the floor first because it has an initial velocity and the dropped ball does not. b. The dropped ball reaches the floor first because its velocity is only in the y-direction. c. Both balls reach the floor at the same time because they both have the same initial zero y-component of velocity.

c. Both balls reach the floor at the same time because they both have the same initial zero y-component of velocity.

A ball is thrown straight upward. At the very top of its flight, the velocity of the ball is zero. Is its acceleration at this point also zero? Explain. a. Yes, the acceleration is zero because the velocity is also zero. b. Yes, the acceleration is zero because the ball is thrown straight upward. c. No, the acceleration due to gravity is constant even at the top of its flight. d. No, the acceleration is decreasing but will not be zero until the ball lands on the ground.

c. No, the acceleration due to gravity is constant even at the top of its flight.

A ball is thrown straight upward and then returns to the Earth. Does the acceleration change direction during this motion? Explain. a. Yes, the acceleration is in the upward direction as it is thrown straight up and in the downward direction as it returns to earth. b. Yes, the acceleration goes to zero as the ball changes direction then the acceleration increases back to its original magnitude. c. No, the acceleration due to gravity is in the downward direction throughout the entire motion. d. No, the acceleration due to gravity is always zero since the ball returns to its original position

c. No, the acceleration due to gravity is in the downward direction throughout the entire motion.