drowning_pocoyo
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- Apr 15, 2009
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- 2010
Hey gys having trouble with another motion question...i did it but not sure if im right can u guys check it. This question doesnt conserve momentum which is kinda weird so im kinda confused. Thanx
A truck mass 7000kg travelling at 100km/h collides with a stationary vehicle of mass 1000kg. The combined mass coalesces and moves off at 30km/h.
(a) Caluculate the amount of energy transferred to the car.
(b) Calculate the efficiency of which kinetic energy is conserved.
Heres what i did:
(a)
Of the car:
Eki = (mv^2) / 2, where Eki = initial kinetic energy
Eki = 0.5 x 1000 x 0
Eki = 0
Ekf = (mv^2) / 2, where Ekf = final kinetic energy
Ekf = 0.5 x 1000 x (30/3.6)^2
Ekf = 34722 J
Hence, the energy transferred to it is: Ekf - Eki = 34722J
(b)
Of the whole system:
Eki = (mt vt^2) / 2 + (mc vc^2) / 2
Eki = 0.5 x 7000 x (100/3.6)^2 + 0.5 x 1000 x 0
Eki = 2700617 J
Eki = 2701 kJ
Ekf = 0.5(mt + mc)v
Ekf = 0.5(8000) x (30/3.6)^2
Ekf = 277778 J
Ekf = 278 kJ
.: Efficiency = 277778/2700617
Efficiency = 10.3%
Have i done it correctly? Thanx again.
A truck mass 7000kg travelling at 100km/h collides with a stationary vehicle of mass 1000kg. The combined mass coalesces and moves off at 30km/h.
(a) Caluculate the amount of energy transferred to the car.
(b) Calculate the efficiency of which kinetic energy is conserved.
Heres what i did:
(a)
Of the car:
Eki = (mv^2) / 2, where Eki = initial kinetic energy
Eki = 0.5 x 1000 x 0
Eki = 0
Ekf = (mv^2) / 2, where Ekf = final kinetic energy
Ekf = 0.5 x 1000 x (30/3.6)^2
Ekf = 34722 J
Hence, the energy transferred to it is: Ekf - Eki = 34722J
(b)
Of the whole system:
Eki = (mt vt^2) / 2 + (mc vc^2) / 2
Eki = 0.5 x 7000 x (100/3.6)^2 + 0.5 x 1000 x 0
Eki = 2700617 J
Eki = 2701 kJ
Ekf = 0.5(mt + mc)v
Ekf = 0.5(8000) x (30/3.6)^2
Ekf = 277778 J
Ekf = 278 kJ
.: Efficiency = 277778/2700617
Efficiency = 10.3%
Have i done it correctly? Thanx again.