Question

A grasshopper jumps straight up from the ground with an initial vertical velocity of 8 feet per second. After how many seconds will the grasshopper be 1 foot off the ground?

A squirrel is 27 feet up in a tree and tosses a nut out of the tree with an initial vertical velocity of 6 feet per second. The squirrel climbs down the tree in 2 seconds. Does it reach the ground before the nut?


I don’t get the process of solving these types of problems please help me?

Answer 1

Problem 1 : After 0.25 s

Problem 2 : The squirrel doesn't reach the ground before the nut

Explanation:

Problem 1

This is a standard physics problem

The equation that defines the movement of the grasshopper given the initial velocity, and the acceleration is the following

Distance = Do + Vo*t + 0.5*a*t^2

Where

Do is the initial distance.

(Do = 0, because the grasshopper is on the ground and we choose the reference system there)

Vo is the initial velocity = 8 feet/sec

a is the acceleration that is exerted on the body (in this case a = g = -9.8 m/s^2 = - 32.174 feet per second per second.)

t is the time

We substitute in the equation, and solve for t (time)

Distance = Do + Vo*t + 0.5*a*t^2

(1 foot)= (0)+ (8 feet/s)*t + 0.5*(-32.174 feet/s^2)*t^2

Solving this equation, we get that

t = 0.25 s

Problem 2

This problem is similar to the previous one

We apply the same formula

D = Do + Vo*t + 0.5*a*t^2

But in this case, we are going in the opposite direction, and we have an initial distance.

Do = 27 feet

Vo is the initial velocity of the nut = -6 feet/s

D = 0 (Ground)

We substitute in the equation, and solve for t (time)

(0) = (27) + (-6 feet/s)*t + 0.5*(-32 feet/s^2)*t^2

t = 1.125 s < 2s

The nut reaches ground in 1.125 s, so the squirrel doesn't reach the ground before the nut