You may neglect friction between the car and floor. (a) What impulse is imparted by this force? (b) Find the final velocity of the bumper car if its initial velocity was 2.80 m/s and the car plus driver have a mass of 200 kg. Professional Application. Suppose a child drives a bumper car head on into the side rail, which exerts a force of 4000 N on the car for 0.200 s.(d) Discuss the implications of your answers for parts (b) and (c). (b) What is the opponent’s final velocity, if his mass is 105 kg and he is motionless in midair when struck near his center of mass? (c) Calculate the recoil velocity of the opponent’s 10.0-kg head if hit in this manner, assuming the head does not initially transfer significant momentum to the boxer’s body. (a) Calculate the impulse imparted by this blow. Professional Application. A professional boxer hits his opponent with a 1000-N horizontal blow that lasts for 0.150 s.(a) What is the average force exerted on the leg, taking the effective mass of the hand and forearm to be 1.50 kg? (b) Would the force be any different if the woman clapped her hands together at the same speed and brought them to rest in the same time? Explain why or why not. A person slaps her leg with her hand, bringing her hand to rest in 2.50 milliseconds from an initial speed of 4.00 m/s.Calculate the force the seat belt exerts on a passenger in the car to bring him to a halt. Professional Application. A car moving at 10 m/s crashes into a tree and stops in 0.26 s.What is the average force exerted on a 0.0300-kg bullet to accelerate it to a speed of 600 m/s in a time of 2.00 ms (milliseconds)? A bullet is accelerated down the barrel of a gun by hot gases produced in the combustion of gun powder.Thus the impulses and their effects are the same for both the actual and effective forces. That area is equal to the area inside the rectangle bounded by F eff, t 1, and t 2. The area under the curve has units of momentum and is equal to the impulse or change in momentum between times t 1 and t 2. Figure 1 shows a graph of what an actual force looks like as a function of time for a ball bouncing off the floor. It is, however, possible to find an average effective force F eff that produces the same result as the corresponding time-varying force. Forces vary considerably even during the brief time intervals considered. Our definition of impulse includes an assumption that the force is constant over the time interval Δ t. Making use of Newton’s third law, the force on the wall due to each ball is normal to the wall along the positive x -direction. The direction of impulse and force is the same as in the case of (a) it is normal to the wall and along the negative x-direction. Quantitatively, the effect we are talking about is the change in momentum Δp.īy rearranging the equation =1.155\\ Discussion For example, if the ball were thrown upward, the gravitational force (which is much smaller than the tennis racquet’s force) would eventually reverse the momentum of the ball. A small force could cause the same change in momentum, but it would have to act for a much longer time. In Example 1 in Linear Momentum and Force, a very large force acting for a short time had a great effect on the momentum of the tennis ball. The effect of a force on an object depends on how long it acts, as well as how great the force is.
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