A wooden sled is being pulled over level snow

PHYSICS · Multi-part · A Level · Physics · Mechanics and materials · Mechanics and materials

Problem

A wooden sled is being pulled over level snow. Two students exert forces F1=(100 ı^+60 ȷ^) N\mathbf F_{1}=\bigl(100\,\hat{\imath}+60\,\hat{\jmath}\bigr)\,\text{N} and F2=(−30 ı^+90 ȷ^) N\mathbf F_{2}=\bigl(-30\,\hat{\imath}+90\,\hat{\jmath}\bigr)\,\text{N}. Kinetic friction on the sled opposes motion with a force Ff=(−50 ı^−40 ȷ^) N\mathbf F_{\mathrm f}=\bigl(-50\,\hat{\imath}-40\,\hat{\jmath}\bigr)\,\text{N}. At the instant considered, the sled moves with velocity v=(4 ı^+3 ȷ^) m s−1\mathbf v=\bigl(4\,\hat{\imath}+3\,\hat{\jmath}\bigr)\,\text{m\,s}^{-1}. (i) Determine the net force acting on the sled. (ii) Calculate the instantaneous power associated with the net force. (iii) State whether mechanical energy is being supplied to or removed from the sled at this instant, giving a reason for your answer.

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