Question

Q. A boy of 50kg hops with a horizontal velocity of 5m/s on stationary skateboard. The skateboard weights 4 kg . Find the velocity when the board starts rolling.​

Answer 1

Answer:

The velocity when the board starts rolling is 4.62 m/s.

Explanation:

Given,

A boy of 50kg hops with a horizontal velocity of 5m/s on stationary skateboard. The skateboard weights 4 kg.

To find: The velocity when the board starts rolling.​

Solution:

Let the velocity when the board starts rolling be 'v' m/s.

We can apply momentum conservation here,

i.e m₁u₁ + m₂u₂ = v(m₁+ m₂)

here, m₁ = 50 kg, u₁ = 5 kg , m₂ = 4 kg, u₂ = 0

Susbtituting the values,

50 × 5 + 4 × 0 = v(50+4)

or, 250 + 0 = v × 54

or, 250 = 54v

or, v = 250/54

or, v = 4.62 m/s

Therefore, The velocity when the board starts rolling is 4.62 m/s.

Answer 2

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Momentum Problem

Given:

m1 = 50 kg

v1 = 5 m/s [E]

m2 = 20 kg

v2 = 1.5 m/s [E]

v3 = final velocity

Foemula:

m1v1 + m2v2 = (m1 + m2) x v3

We need to find v3

v3 = (m1v1 + m2v2) / (m1 + m2)

= (50x5 + 20x1.5) / (50 + 20)

= 280 / 70

= 4 m/s [E]

The final velocity is 4 m/s [E].

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