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This action will lengthen the time of impact between the ball and the glove and further reduce the impulsive force acting on his palm. (b) When catching the ball, the player moves his hand backward. (a) The glove which is made of soft material lengthens the time of impact and reduces Figure shows a baseball player stopping a fast moving ball with his hand.The loose sand lengthens the time of impact and reduces the impulsive force acting on him. A long jumper lands on a pit filled with loose sand.The impulsive force acting on the high jumper is reduced and he is less likely to suffer any injury. When a high jumper falls on a mattress, the thick and soft mattress lengthens the time of impact.Increasing the time of impact, t to reduce the impulsive force, F Hence, by controlling the value of f, we can control the value of the impulsive force, F. The longer the time of impact, the smaller the impulsive force. Since F ∝ 1/t, the shorter the time of impact, the bigger the impulsive force. If the change of momentum is constant, the magnitude of the impulsive force is inversely proportional to the time of impact. = 250 kg × (6) m/s 2 = 1500 N The Effect of Time on the Magnitude of the Impulsive ForceĬonsider the formula for impulsive force: The magnitude of the force applied by the brakes is given by the equation, Therefore, the acceleration of the motorcycle,
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The change in the velocity of the motorcycle in 5s = 0 – 30 = –30 m/s Time taken to stop = 5s, the mass of the motorcycle with rider = 250 kg. Solution: Given that initial velocity of the motorcycle Calculate the force exerted by the brakes on the motorcycle if its mass along with the rider is 250 kg. (The negative sign shows that the force is applied in a direction opposite to the direction of motion of the ball).Įxample 6. A motorcycle is moving with a velocity of 108 km/hr and it takes 5 s to stop it after the brakes are applied. Since it moves a distance of 4 m in 1 s, therefore, its uniform velocity = 4m/s. Solution: When the force ceases to act, the body will move with a constant velocity. The force then ceases to act and the body moves through 4m in the next one second. (c) From the answers in (a) and (b), what is the relationship between the time of impact and the impulsive force?Įxample 3. A force acts for 0.2 s on a body of mass 2.5 kg initially at rest. What is the impulsive force exerted on the rock? However, due to the rigidity of the rock, the time which the foot acts on the rock is only 0.01 s. (b) The boy then kicks a rock of the same mass and it moves from rest to 15 m s -1. Calculate the impulsive force exerted on the ball. (a) From Figure, when the boy kicks the 1.2 kg football, it moves from rest to 15 m s -1 in 0.1 s. Figure shows a boy kicking a football and a rock. (The negative sign shows that the force is acting against the initial direction of motion of the ball)Įxample 2. (b) the impulsive force exerted on the ball by the hands. The time of contact between the hand and the ball is 0.05 s. Figure shows the magnitudes of its velocity before and after being hit respectively. A boy hits a 0.50 kg ball and sends it moving in the opposite direction. Impulse of Force Example Problems with SolutionsĮxample 1. By doing so he increases the time interval to reduce the momentum of the ball. Cricket ball coming towards fielder has a large momentum. Hence, impulsive force is defined as the rate of change of momentum.Įxample: While catching a cricket ball a player moves his hands backwards.The force is known as the impulsive force. Impulse is a vector quantity and has the same direction as the applied force.The SI unit for impulse is newton seconds (N s).The quantity (Force x Time) is called the impulse of a force.If a force F is applied on a body of mass m for a time interval Δt and if the change in velocity is Δv then Or force is equal to the rate of change of momentum. Since (mv – mu) is the change of momentum, therefore, By definition, acceleration, a is the rate of change in velocity and is given by the formula: When a net force acts on a body, it accelerates in the direction of the force. From the previous section, you have seen that Newtons Second Law can be summed up by the formula F = ma.