1. _____ A ball is dropping from the top of a building. Ignoring air resistance,
ID: 1369667 • Letter: 1
Question
1. _____ A ball is dropping from the top of a building. Ignoring air resistance, which of the following quantities will decrease?
(A) Mechanical energy (B) Kinetic energy (C) Potential energy (D) Acceleration
2. A system is consisting of two masses: m1 of 3.0 kg moves to left at 2.0 m/s and m2 of 5.0 kg moves to right at 4.0 m/s. What is the total kinetic energy of the system?
3. Block A of mass 3.0 kg slides into block B of mass 2.0 kg. Before collision, block A moves to the right with speed 10.0 m/s, and block B moves to the right with speed 5.0 m/s. After collision, block A moves to the right with speed 6.0 m/s. (a) What is the velocity of block B after collision? (b) What is the kinetic energy change for the system?
Explanation / Answer
1) (C) Potential energy
2) Total KE = KE1 +KE2
= 0.5*3*2^2 + 0.5*5*4^2
= 46 J
3)
Let
m1 = 3kg
m2 = 2kg
u1 = 10 m/s
u2 = 5 m/s
a) V2 = ((m2-m1)*u2 + 2*m1*u1)/(m1+m2)
= ( (2 - 3)*5 + 2*3*10)/(3+2)
= 11 J
b) KE2 - KE1 = (0.5*m1*u1^2 + 0.5*m2*u2^2) - (0.5*m*v1^2 + 0.5*m2*v2^2)
= (0.5*3*10^2 + 0.5*2*5^2) - (0.5*3*6^2 + 0.5*2*11^2)
= 0 J
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