# Need help in physics, can anyone explain these two problems? ?

1. The figure below shows a roller coaster cart and a track. The cart is 250 kg and it starts the motion from rest at A. What is the speed of the cart at point B?

a) 98 m/s

b) 196 m/s

c) 14 m/s

d) 10 m/s

a) What is the speed of the cart at point C?

a) 98 m/s

b) 196 m/s

c) 14 m/s

d) 10 m/s ### 2 respuestas

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• Respuesta preferida

(A) By the law of energy conservation:

=>KE(B) + PE(B) = KE(A) + PE(A)

=>KE(B) - KE(A) = PE(A) - PE(B)

=>1/2mv^2 - 0 = mghA - mghB

=>1/2mv^2 = mg(hA -hB)

=>1/2mv^2 = mg∆h

=>v = √2g∆h

=>v = √[2 x 9.81 x 5]

=>v = 9.90 m/s ≈ 10 m/s

=>(d)

(B) =>v = √2g∆h

=>v = √[2 x 9.81 x 10]

=>v = 14 m/s

=>(c)

• 1. The figure below shows a roller coaster cart and a track. The cart is 250 kg and it starts the motion from rest at A.

1.1 What is the speed Vb of the cart at point B?

Vb = √ 2*g(ha-hb) = √ 2*10*5 = √ 100 = 10 m/sec , no matter the mass m

1.2  What is the speed Vc of the cart at point C?

Vc = √ 2*g(ha-0) = √ 2*10*10= √ 200 = 14 m/sec , no matter the mass m

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