Question

You are pulling your sister on a sled across the flat field. Your sister and the sled have a total mass of 50 kg. You pull the sled, from starting to rest, with a constant force of 79 N at and angle of 45 degrees. What will the speed of the sled be when you reach 11.1 m from the start? If the coefficient of friction between the sled and a now is .15 what will the speed of the sled be when you reach 19.0 m from the start?

Answer 1

Case i) There is no frictional force acting on the sled.

The acceleration of the sled when a force of 79 N is acting at an angle of 45⁰ is given by

where M is the mass of the sled +person.

At a distance of 11.1 m from the start,. Therefore the final velocity of the sled in the positive direction i.e to the right.

Case ii) There is a frictional force acting.

The frictional force opposing the horizontal force is given by where is the coefficient of friction and R is the reaction force.

Therefore, the total force acting on the sled= on substituting the values of M,, and g.

Therefore the acceleration of the sled=F₁/M=-9.22/50=-0.18 m/s².

Thus the sled decelerates at a rate of 0.18 m/s².

Thus, at a distance of 19 m from the start, .

i.e the velocity of the sled is in a negative direction i.e to the left.