PHYSICS worries about the CAUSES of MOTION. APPLIED MATHEMATICS worries about th
ID: 2037644 • Letter: P
Question
PHYSICS worries about the CAUSES of MOTION. APPLIED MATHEMATICS worries about the DESCRIPTION of MOTION. Whereas in PHYSICS we start with equations that relate the ACCELERATION to FORCES, in KINEMATICS an acceleration is just a FUNCTION of TIME.
1. A pump sprays water out of a tank on a cart weighing 185 kg. The tank contains 52 kg, and the pump sprays out water at a rate of 2.32 kg/s that leaves with a speed of 2.7 m/s relative to the cart. The cart starts from rest.
(a) Use conservation of momentum to find the speed of the cart after the pump has been running for 8 s.
(b) What is the force on the cart at that time?
Explanation / Answer
a)
Mass of water sprayed for t=8 s
MW =2.32*8 =18.56 Kg
reamaining water
m=52-18.56 =33.44 Kg
By Conservation of momentum
Pi = Pf
0 = (185+33.44)*VC -(18.56)*2.7
VC=0.2294 m/s
b)
F=VdM/dt =(2.7-0.2294)*2.32
F=5.73 N
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