Question

An 87-kg running back leaps straight ahead toward the end zone with a speed of 6.2 m/s. A 115-kg linebacker, keeping his feet on the ground, catches the running back and applies a force of 818 N in the opposite direction for 0.71 s before the running back's feet touch the ground. (a) What is the impulse that the linebacker imparts to the running back? magnitude_____ direction______(in the direction of the running back's initial motion or in the direction of the linebacker's initial motion) (b) What change in the running back's momentum does the impulse produce? magnitude_____ direction______(in the direction of the running back's initial motion or in the direction of the linebacker's initial motion) (c) What is the running back's momentum when his feet touch the ground? magnitude_____ direction______(in the direction of the running back's initial motion or in the direction of the linebacker's initial motion) (d) If the linebacker keeps applying the same force after the running back's feet have touched the ground, is this still the only force acting to change the running back's momentum? Yes or No

Answer 1

Part A)  the impulse that the linebacker imparts to the running back, as per definition

in the direction of the linebacker's initial motion

Part B) The change in the running back's momentum does the impulse produce using Impulse momentum theorem

in the direction of the linebacker's initial motion.

Part C) the running back's momentum when his feet touch the ground

so magnitude is in the direction of the linebacker's initial motion

Part D) No, Force of friction also acts on the running back to change the running back's momentum