Question

1. How much work is required to extend an exercise spring by 45 cm if the spring constant k has the value 310 N/m?   J

What force is required to extend the spring by 45 cm?

2. A horizontal force T of 100 N is applied to a box of books of mass 20 kg resting on a wooden table.   If the coefficient of friction of the box on the table is 0.40, the friction force is___ N.   If the box moves, its acceleration is ____ m/s².

3. A ball is thrown into a net 39.0 m away. The ball is thrown with a speed of 38.0 m/s at a height of 1.50 m from the ground and making an angle of 20.0⁰ with the horizontal. The ball will be ______ meters high when it gets to the net.

4. Suppose you get into your car and travel 25 km due north. Then you turn and travel an unknown distance east. Finally you travel 32 km directly back to your starting point. How long was the eastern leg of your trip?

Answer 1

1. Work = 0.5 kx²= 0.5×310×(0.45)²=31.4Joules

Force (F=)= Kx = 310×0.45 = 139.5 N

2.frictional force (Fk ) = mg = 0.4×20×9.8 = 78.4N

Net force (F) = ma = 100-78.4=21.6N

Acceleration (a) = 1.08 m/s²

3. Time to reach the net (t) = 39/(38×cos(20)) = 1.092sec

Vertical displacement = vy t+0.5 at²

Y-1.5= 38×sin20 ×1.092 -0.5×9.8×(1.092²)

Y-1.5= 8.35m

From ground it will hit the net at (y) =9.85m

4. Eastern distance=

square root of (32²-25²) =19.975 km