Question

1) A 90.0-N box is pulled 10.0 m along a level surface by a rope. If the rope makes an angle of 20.0° with the surface, and the force exerted through the rope is 75.0 N, the work is done on the box is ___J.

2) A 25.0-N object is held 2.10 m above the ground. The potential energy of the object with respect to the ground is ___J.

3) The kinetic energy of a 20.0-N object is 5.00 × 10² J. The speed of this object is ___m/s.

4) A 10.0-N object is accelerated uniformly from rest at a rate of 2.5 m/s². The kinetic energy of this object after it has accelerated a distance of 15.0 m is ___J.

Answer 1

1)

$$W=(75)(10)\cos{20}=705\ J$$

2)

$$U=(25)(2.1)=52.5\ J$$

3)

$$0.5\frac{20}{9.8}v^2=500\\v=22.1\frac{m}{s}$$

4)

$$K=\frac{10}{9.8}(2.5)(15)=38.3\ J$$