3. A van of mass 1600 kg is moving with constant speed down a straight road inclined at \(7 ^ { \circ }\) to the horizontal. The non-gravitational resistance to the van's motion has a constant magnitude of 2000 N and the engine of the van is working at a rate of 1.5 kW . Find
- the constant speed of the van,
- the acceleration of the van if the resistance is suddenly reduced to 1900 N .