A contestant in a winter games event pushes a 60.0-kg rock across a frozen lake

Question

A contestant in a winter games event pushes a 60.0-kg rock across a frozen lake with a force of 25 N at 30? below the horizontal as shown in Figure (a) below, and it moves with an acceleration of 0.36 m/s2 to the right. (a) What is the normal force exerted by the lake surface on the rock? N (b) Instead of pushing on the rock, the contestant now pulls on it with a rope over his shoulder at the same angle above the horizontal as in part (a). See Figure (b) above. Now what is the normal force exerted by the lake surface on the rock? N

Explanation / Answer

N = mg + Psin30 = 60*9.8 + 25sin30 = 600.5 N (b) N = mg-Psin30 = 575.5 N

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