A skateboarder is coasting due north across a level plaza at a constant speed of…
PHYSICS · Multi-part · A Level · Physics · Mechanics and materials · Mechanics and materials
Problem
A 60kg skateboarder is coasting due north across a level plaza at a constant speed of 3.0ms−1 relative to the ground. The skateboarder suddenly throws a 2.0kg camera directly forward (due north) with a speed of 5.0ms−1 relative to the skateboarder at the instant of release. Assume the skateboarder’s speed relative to the ground does not change appreciably during the brief throw and neglect air resistance.
(a) Determine the camera’s speed relative to the ground immediately after release.
(b) Calculate the camera’s translational kinetic energy as measured by (i) the skateboarder and (ii) a stationary observer on the ground.
(c) Compute the numerical difference between the kinetic-energy values obtained in part (b).
(d) Explain, using clear reasoning, why the ground observer calculates a larger value for the camera’s kinetic energy than the skateboarder does, even though both observers agree on the camera’s mass.