A 5 kg ball is thrown straight up in the air with an initial speed of 15 m/s. Wh
ID: 1996979 • Letter: A
Question
A 5 kg ball is thrown straight up in the air with an initial speed of 15 m/s. What is the momentum of the ball at: the beginning, half way up, maximum height? What is the impulse delivered to a 0.1 kg ball that is initially at rest, and reaches a speed of 5 m/s after it is struck? What is the moment of inertia of a disk, cylinder, and sphere rotating about an axis through their center? Let the mass and radius of each be 5 kg and 2 m respectively. What is the angular momentum of the disk, cylinder, and sphere mentioned in question 3, rotating at 5 rads/s about an axis through their centers? In a hurry to catch a cab, you rush through a frictionless swinging door and onto the sidewalk. The force you exerted on the door was 50 N, applied perpendicularly to the plane of the door. The door is 1 m wide. Assuming that you pushed the door at its edge, what was the torque on the door with its hinge as the pivot?Explanation / Answer
(1). Mass m = 5 kg
Initial velocity u = 15 m/s
Maximum height reached H = u 2 / 2g
= 15 2 / (2x9.8)
= 11.47 m
Let the Velocity at half way be v .
Initial velocity u =15 m/s
Distance trvael S = H / 2 = 11.47 / 2 = 5.739 m
Accleration a = -g = -9.8 m/s 2
From the relation v 2 - u 2 = 2aS
v 2 - 15 2 = 2(-9.8)(5.739
v 2 = 225 - 112.5
= 112.5
v = 10.6 m/s
(a).momentum of the ball at the begining P = mu = 5(15) = 75 kg m/s
(b). Momentum of the ball at halfway up , P ' = mv = 5(10.6) = 53 kg m/s
(c). Momentum of the ball at the top , P " = mV
Where V = Velocity of the ball at the top = 0
So, P " = m(0) = 0 kg m/s
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