Question

A metal rod (weight = 100 N) is resting on a skateboard and leaning against a wall (as in the figure). The skateboard would be free to roll except that it is attached to the wall with a spring (k= 1000 N/m), which happens to be stretched by 2.5 cm beyond its relaxed length. Assume the wall exerts no friction force on the rod, but that there is friction between the rod and the skateboard. Use the drop-down lists to answer the questions:

What is the normal force from the skateboard on the rod (in N)

What is the normal force from the wall on the rod (in N)?

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Answer 1

Net vertical force on the rod must be zero other than it's weight there can only be one vertical force on the rod which is normal reaction from the skateboard. Hence normal reaction from the skateboard on the rod = 100 N, upwards

Taking rod and skateboard as a system, for equilibrium net force on the horizontal direction must be zero hence normal force from the vertical wall must balance the force applied by the spring which is equal to KX = 1000 * 0.025 = 25 N

Hence normal force from the wall on the rod = 25 N , towards right.