Subtraction of Numbers

1) Neeta Puts Two Balls, A, and B, of Weight 15 Each in the Different Swimming Pools. The Upthrust on Ball A Was 12 gf, and the Upthrust on Ball B Was 18 gf. Which Ball Will Float, and Which Will Sink? Explain.

The weight of the ball A = 15 gf
Upthrust on the ball A = 12 gf
Here, 12 < 15
Since the upthrust on ball A is less than the weight of ball A (U < W).
Therefore, ball A will sink.
The weight of the ball B = 15 gf
Upthrust on the ball B = 18 gf
Here, 18 > 15

Since the upthrust on the ball B is more than the weight of the ball B (U > W). Therefore, ball B will float.

2) The object’s weight in the Water and the Air Is 18 Kgf and 8 Kgf, respectively. Find the Upthrust That Will Act on the Object When Placed in Water.

We know that W_L = W_A – U. From this formula, it follows that
U = W_A – W_L
Substitute 18 for W_A and 8 for W_L in the formula U = W_A – W_L
and then subtract to get the upthrust.
U = 18 – 8
 = 10 Kgf
Thus, the upthrust due to the water is 10 Kgf.

3) A Wooden Block Weight 12 GF Was Placed in Water. An Upward Force Acting on the Wooden Block Due to the Water Is 4 GF. Find the Weight of the Wooden Block in the Water.

Weight of the wooden block in the air = 12 gf
Upthrust due to water = 4 gf.
The formula to calculate the body’s weight in liquid is
W_L = W_A – U, where
W_L = Body’s weight in liquid
W_A = Body’s weight in the air
U = Upthrust due to liquid.

Substitute 12 for W_A and 4 for U in the formula W_L = W_A – U and then simplify to get the weight of the wooden block in the water.
W_L = 12 – 4
   = 8

Therefore, the weight of the wooden block in the water is 8 gf.