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WORK, ENERGY and POWER
 1. A vehicle of mass 1500kg is moving at 50kmh-1. The brakes are applied, producing a constant force of 2500N. Ignoring all other forces, calculate the distance moved by the vehicle during braking. 2. a) A small metal ball of mass 5×10-3kg , rests on a spring, of elastic constant, k=500Nm-1. The ball is pushed down 2cm from its equilibrium position and then released (see diagrams below). Calculate the height to which the ball will rise. Ignore friction and air resistance. b) In a similar experiment, the same ball is projected by the same spring as shown below. Again the spring is compressed 2cm and the ball is released. At its maximum height, it is found to be moving at 4ms-1. Calculate the maximum height, h. Ignore friction and air resistance. 3. A person is using a bow to shoot an arrow. The person displaces the centre of the bow-string 50cm from its equilibrium position. When at this displacement, the person exerts a force of 160N on the string. The arrow has a mass of 100g. Estimate the speed with which the arrow leaves the bow. 4. An elevator motor is moving an empty elevator at a speed of 2ms-1, see diagram below. The electrical power input to the motor is 2kW. The motor is 60% efficient. Calculate the magnitude of the force (friction plus air resistance) against which the motor is working.

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