A body was moving uniformly under the effect of three forces , , and . Given that and , where and are orthogonal unit vectors, determine which ensures that it will move at a constant velocity.
A car of mass 1.8 tonnes is moving at a constant speed on a horizontal road. If the resistance to the motion is 57.6 kg-wt per tonne of the car’s mass, find the force of its motor.
A train of mass 50 tonnes has an engine whose maximum driving force is 9 000 kg-wt. Given that the resistance to its motion due to friction is directly proportional to the square of its speed and that this resistance was 20 kg-wt for each tonne of the train’s mass when its speed was 75 km/h, find the maximum speed of the train.