Question

A 25 kg child goes down a straight slide inclined 38 degrees above horizontal. The child is acted on by his weight, the normal force from the slide, and kinetic friction.

How large is the normal force of the slide on the child?

Express your answer to two significant figures and include the appropriate units.

Answer 1

Concepts and reason

The concepts used to solve this problem are normal force and force due to gravity.

Use force due to gravity to find the normal force on the child.

Fundamentals

Normal force is the force exerted by the surface to the body in the direction normal to the surface.

Gravitational force is an attractive force, and it is always present between two masses.

The force at which the earth attracts a body is known as weight of the body or force due to gravity, and its expression is

Here, mass of the body is , acceleration due to gravity is , and gravitational force is .

Free body diagram is shown below.

Expression for force of gravity is

Substitute for in the above expression. So the gravitational pull on the child in the vertically downward direction is

Here, the mass of the child is .

The straight surface is inclined at an angle with the horizontal.

Then, from the figure, the normal of the surface is at an angle from the vertical axis.

The component of gravitational pull along the normal direction is

Here, the normal force is .

Substitute for in the above expression.

The expression for the normal force is

Substitute for , for , and for .

Ans:

The normal force on the child is .