Physics Help Forum displacement, velocity,acceleration

 Kinematics and Dynamics Kinematics and Dynamics Physics Help Forum

 Mar 4th 2009, 10:27 PM #1 Junior Member   Join Date: Feb 2009 Posts: 18 displacement, velocity,acceleration how the displacement of vertically thrown ball varies with time? how the velocity of vertically thrown ball varies with time? a car accelerates along the road. which force actually moves the car? Which will be more effective in knocking the bear down. 1)a rubber bullet or 2)a lead bullet of the same momentum
 Mar 5th 2009, 08:18 PM #2 Senior Member   Join Date: Feb 2009 Location: Singapore Posts: 206 use the equation:$\displaystyle s = ut + 0.5at^2$ second one use the equation:$\displaystyle v = u + at$ for a car accelerating on a road, assuming the road is horizontal, the force provided by the engine to the wheels moves the vehicle frictional forces and air resistance act in the opposite direction. there was a post on this quite recently. the rubber bullet would bounce off the bear, by the law of the conservation of momentum, this would mean the bear has to move in the direction that the bullet hit it with greater momentum to compensate for the bullet's opposite momentum in bouncing off the bear. the lead bullet would either go through or embed itself in the bullet and this would mean the velocity of the bear after the collision would be lower. therefore, the rubber bullet would be more effective in knocking down the bear. but in reality the lead bullet would have greater effect in bringing the bear down.

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### how the displacement of a vertically thrown ball varies with time with graph

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