There are 4 forces acting on the block:
• its weight (magnitude w = m g = 98 N, where m = 10 kg and g = 9.80 m/s²), pointed downward
• the normal force (mag. n), pointed upward
• friction (mag. f = 15 N), pointing opposite the direction of motion
• the pulling force (mag. p = 75 N), pointing at a 20° angle with the positive horizontal direction
Let the direction in which the block is being pulled be the positive horizontal direction, and upward the positive vertical direction. Split up each force into their horizontal and vertical components, then apply Newton's second law. We have a net horizontal force of
∑ F = p cos(20°) - f = m a
where a is the acceleration of the block. The net vertical force is 0, since the block gets dragged along the surface and doesn't move up or down (presumably).
Solve for a :
(75 N) cos(20°) - 15 N = (10 kg) a
a ≈ 5.4 m/s²
